For what it's worth...

I have been using this configuration to record multiple instruments, multiple tracks (typically 8-24) on the following configuration.

HP Pavilion with AMD (Athlon) 64 X 2 Dual Core Processor 4400+, 2.19 Ghz Processors, which is about 3 years old
2 GB ram
Windows XP Media Edition, Service Pack 2
Dual internal disk drives (500MB ea, one for O/S, applications, and one for audio)
Cakewalk Sonar Studio 5 (latest version available is 8)
Presonus Firepod (firewire), ten ch, Edirol FA-66, six channel(firewire)
Several soft synths, a pair of hardware synths/keyboards

I use BB to lay down ideas, and export that (midi/audio) to Sonar, and do all my instrument recording, mixing, etc. in Sonar. One can certainly use BB or RealBand (or PowerTracks Pro) to record instruments, mix, etc. However, I find that for my projects, I like the ability to bring in any number of synths, instruments, etc. Sonar provides me with that ability. Not to say you can't do it with BB, Realband (but you are limited to one Synth at a time), or others, but this is what I use. And, I can also run Sonar on a lap top (1.25 GB ram, single processor under 2 GHz.

I also have hardware multitrack recorders I use for live situations, and they afford other benefits, such as hands on multi-channel controls, etc. But for studio, I use my PC. I like the additional graphic views and more powerful/easier to use editing than most hardware recorders affort.

Depending on the other specs of you PC, you should be able to even use RealBand to do what you want. A suggestion, is to make sure no other applications are running, including antivirus/spyware utilities, as they can really hog system resources.