Bristol_Jonesey
I disagree, for all of the reasons outlined above by myself and others

Not sure what you're referring to, but the specs I based my opinion off of are:
model: ixtremeM3720 rating 3.3
processor: intel (R) Core (TM)2 Quad Pro Q8300  @2.50 GHz 2.50GHz
RAM 4.00GB (3.75 usable)
 
If that's correct then for the OP's stated needs of writing a few soft synth tracks and recording vocals, he has more than enough power.  He just needs to make sure he has a decent interface with the right drivers.  Buying a new computer certainly won't hurt but it's unnecessary.

I tend to agree with rlared.  People have done a lot more complicated work than you are talking about with a lot less computer.  You may be able to achieve your goals with what you already have, but with some performance tuning (turn off WIFI, better driver for audio interface, etc).  Find out where things are failing before tryibg to figure out what to replace.
 
Glen

gcolbert
People have done a lot more complicated work than you are talking about with a lot less computer.

And if you manage to swing an RME Babyface interface, you'll be happy for years.
 
Spend the rest on acoustic treatment of your space.  Worry about the computer later.
 

IMHO you need a 64 bit OS, cuz you need 4 gigs of usable ram minimum.  If you don't, then you will be utilizing your swap file (hard drive fake memory) and then be posting here complaining about pops and clicks.  Probably 8 gigs is the minimum.
 
You need a cpu that is on the "high end" cpu list on cpubench site. 
 
As far as AtoD cards, I don't get the M-audio bashers.  I've had a Delta44 for years and years and the thing works flawlessly.  I also have an M-track still in the box that I've never used.  Bash not.
 
 

The Delta series was pretty good. The Fast Track Pro is not. 

I have an Atom-powered laptop that records 28 tracks live simultaneously over two Tascam interfaces (US-1800 and US-1641) through ASIO4All - the worst possible setup. And it has worked great for years.
 
So if that works, your computer is fine.
 
Where things will become problematic is when you start using plug-ins and then nobody can say how much power is enough because each plug-in is different. But Sonar is a mature product with helpful tricks for those older machines. For example you can freeze tracks to save processing power. The plug-in on that track gets converted to an ordinary WAV file and does not use CPU anymore.
 
You will hear warnings about dropouts, etc. If that happens, just increase the buffer size. Dropout problems are usually due to causes unrelated to processing power. Folks here with super-pro machines report dropouts.
 
Latency does not arise when recording vocals or instruments over your interface, only when playing VST plug-in instruments live over a MIDI keyboard. You say you can't play, so that's never going to be an issue for you.
 
One day you may want to get a power machine. You can decide on that later. For now, you're good to go.