Thanks, some really helpful responses.
Right now I'm still using the trial version of Sonar. I imagine I'll probably end up buying the program because I like it despite the very steep learning curve (and I am a previous Cakewalk owner - tho my last version was Cakewalk Pro Audio 4 or something, like 15 years ago). Currently I have it interfaced with my digital piano (Kawai CN34), which has a few hundred built in instruments of varying quality. I had a bunch of old midi files I created with my old version of Cakewalk that I wanted to use as a starting point, so I loaded them into Sonar Trial, and used my CN34's instrument suite for playback through the piano (which I also used to record mp3 files). After a whole lot of tweaking, I've been fairly happy with the results, but some of the instruments on my CN34 I just don't like, notably the cello (sounds like a walrus in pain), some winds, and brass. Also the selection of effects, like pads and leads, is a little limited, so all my songs end up sounding very similar. Honestly, I don't use the digital piano for playing notes into the software. I usually do most of my note input with the mouse, and use the piano only for its sounds. My laptop near my piano (Windows 7 32 bit) also has a very small screen, which is difficult to use with Sonar.
Therefore, what I'd kind of like to do is have Sonar installed on my desktop computer (64 bit windows, with 32 inch screen) and ditch the piano altogether. As has been pointed out, the sounds that come with the sound card just don't cut it. So what I'm looking for is a few hundred good quality instruments and sounds that I can put on my desktop computer so I can run Sonar right from there, using my piano for recording only if I have to.
I tried installing Soft Synths on my cakewalk. When I go that I have under VST2 an option called Cakewalk Sound Center. I tried fiddling with it but I can't hear anything on playback and there doesn't seem to be a whole lot of instruments to be honest. Maybe there are more options with a real version of Sonar?
Also, sorry for the ignorance, but what do you mean by "interface"?
My budget isn't hard capped but I'd like to spend less than $200 to $250 on this (including price of Sonar) since this is really just a hobby for me.
Thanks again for the guidance. I had previously thought Adobe Illustrator and Photoshop were hard to figure out. This audio stuff is even crazier...