BassDaddy
I would defer to the piano experts here but I have a question. Doesn't the 4 GB RAM of 32Bit restrict some sampled instruments? Are any of the ones being talked about modeled? Modeled wouldn't be a problem. If you weren't going to be doing any recording you should be OK but in a project there could easily not be enough room for sampled instruments with all the layers and velocities and articulations sampled.  

Good point your have there, didn't think of that. I guess this must be one of the main advantages modeled- vs sample-based have in a 32 bit environment. 

Thanks to everybody for helpful suggestions. I landed on the Pianoteq Stage ed. Very happy with it. 
 
What I forgot about in my desire for XP compatibility, is that you really need to have a high spec PC
for it to run smoothly, as the module is CPU intensive. My P4 3GHz system had a hard time dealing with it.
Will have to beef up my specs. 

Didn’t know that. Must have changed between updates. Used to be pretty easy on cpu.

Fleer
Didn’t know that. Must have changed between updates. Used to be pretty easy on cpu.

I think the models become more CPU intensive with versions. I would say there is also a noticeable improvement in sound as a consequence. I got CPU overload warnings in pianoteq ... but I wonder if my Presonus Audiobox ASIO XP driver might also be a factor ... I  found it's XP version to be at bit picky with it's clients at times ... and the general CPU meter for the system was never anywhere near the red-zone. Anyway, after contacting Pianoteq support they gave me version 4, which works fine with my XP system.
Regardless ... I'm really happy with the sound in Pianoteq ... it's incredible how enjoyable it is to play with ... and I also have higher performing win7 systems to use ... where CPU isn't an issue. Definitely the best plug-in I have ever bought.  

Enjoy!

The free Addictive Keys Studio Grand is limited to 4 octaves, and has limited microphone placements.
 
But that will fit perfectly well with any 49 key controller, such as the Roland A-500, and sounds great!  It would be an inexpensive way to get a good piano sound even if you opted for an upgrade to the full version.
 
I think that the AD Keys free version is the best sounding piano in my current rig.  I also have the True Pianos Amber, AIR Mini Grand, and the SONiVOX Eighty-Eight Ensemble to compare with.
 
But I would probably go with the Pianoteq if I had an 88 key controller, and was looking for realistic piano performance dynamics.

abacab
The free Addictive Keys Studio Grand is limited to 4 octaves, and has limited microphone placements.
 
But that will fit perfectly well with any 49 key controller, such as the Roland A-500, and sounds great!  It would be an inexpensive way to get a good piano sound even if you opted for an upgrade to the full version.
 
I think that the AD Keys free version is the best sounding piano in my current rig.  I also have the True Pianos Amber, AIR Mini Grand, and the SONiVOX Eighty-Eight Ensemble to compare with.
 
But I would probably go with the Pianoteq if I had an 88 key controller, and was looking for realistic piano performance dynamics.

I tried it, but didn't find it had comparable expressiveness when playing. Sounded well though, with extensive possibility for finding the "right sound". 

iRelevant

abacab
The free Addictive Keys Studio Grand is limited to 4 octaves, and has limited microphone placements.
 
But that will fit perfectly well with any 49 key controller, such as the Roland A-500, and sounds great!  It would be an inexpensive way to get a good piano sound even if you opted for an upgrade to the full version.
 
I think that the AD Keys free version is the best sounding piano in my current rig.  I also have the True Pianos Amber, AIR Mini Grand, and the SONiVOX Eighty-Eight Ensemble to compare with.
 
But I would probably go with the Pianoteq if I had an 88 key controller, and was looking for realistic piano performance dynamics.

I tried it, but didn't find it had comparable expressiveness when playing. Sounded well though, with extensive possibility for finding the "right sound". 

That's why I mentioned that I would probably opt for Pianoteq for realistic piano dynamics.  But since I am not a solo piano player, the "sound" of something like Addictive Keys works just fine for me with layered parts.
 
I watched an extensive demo of a live pianist comparing a number of piano VSTi plugins, and he commented that many modeled pianos played more like real pianos, while some of the sampled pianos sounded more realistic.  So it's probably a matter of finding the best compromise for your needs.
 
But you will probably also want a weighted 88 key controller to achieve a completely realistic piano feel.  You just won't get that with a plastic synth action 49 key controller.
 
Hope you find something that works for you!

Thank you. I'm on the lookout for a 88 keyboard, yes, preferably one with hammer action. Taking my time. 
Although it will make a difference with the "real deal" of course, the ability of Pianoteq to make a match between your existing keyboard and your playing style was real nice, and one of the main advantages it had over Truepianos. A velocity curve is made based on input from your style of playing soft, normal, or hard. 

Funny how you mentioned that installing AD keys was a chore. I guess most of us already have the XLN installer due to having AD2. It was a simple matter of clicking the demo button. 
I had tried a few pianos and demo's and by far the AD keys is the one that cuts through in a rock, country or blues song. I guess it really depends on the music which one you would use. But for free it was a big surprise.
I grabbed the free Electric piano add pack via my Focusrite account so I'm 99% covered piano wise now. 
 
And Air's midi grand is also pretty good, but for me it had a major bug where the reverb would go full blast when I re opened a project. It would change patches even though everything was set to "none" Seems I'm the only one who had this issue according to the user forum.