Get a top notch PC, probably a P4 (turn off hyperthreading) to be safe. Get lots of RAM - at least 1GB, as much as 2GB. Get any old hard drive for the system, another really fast one for the samples, and possibly a third if you record live audio. Get a high quality soundcard that supports GSIF - and possibly GSIF 2. Figure out how many ins and out that you need and that will determine your price range.
If you're doing larger works, definitely get Orchestra. Ensemble for smaller stuff. Solo if money is the top priority.
Then save for additional libraries. You wil never have all that you want.
The big guns are Echo, M-Audio and RME. There's a message about RME card problems with GS3, but that is either a peculiar machine, or will likely be resolved quickly. Tascam also makes some audio cards.
If you're on a budget the Audiophile 2426 is the most popular solution. I prefer the Echo MIA, since it has multiple virtual outputs and balanced 1/4" TRS connections, rather than RCA jacks. As you move upscale the choices are often related to how many ins and outs you need.
Tell us more about what you want to achieve - and what budget you want to achieve it with.
I have to politely disagree on the specs for the PC. Everyone seems to want the biggest, fastest machines, and I used to be like that. But I can't help noticing that my Athlon 1800+ processor and 768 MB of ram will reach 160 polyphony without breaking a sweat.
If you set up your system well, it's not necessary to spend all that extra money on the fastest, newest components.
Not sure what my budget is yet so don't limit any of the suggestions by price range.
Basically, I used to produce Hip Hop - I'm tired of that and all of the bull that goes along with it. I've always had a knack for creating pieces that expressed a certain mood so I'm going to start doing that. I'm not looking to create any particular style of music, I just do what I feel. I have a sizeable library of sounds of all types for my hardware samplers so I'm looking to duplicate that when I convert over to Giga.
Any suggestions that you may have, throw em at me. I will be taking EVERYTHING into consideration.
Vertigo50 makes a good point about not necesarily needing the baddest machine for Giga. It really depends on what you want to do with it. If you're not doing many effects, you don't need much CPU. That was the world of GS2.5. If, on the other hand, you get GS3 Orchestra and plan to use GigaPulse, get as much CPU as you can afford.
RAM is easier, since you can add more in the future if you need it. Basically, RAM determines how many instruments that you can load at once. I was doing a four piece blues band tonight and only needed 4% of the available memory. But once you go for a Wagnerian orchestra and you want to use lots of different articulations, you want 2GB or so.
I used to be of the mind that I could always load up different sounds for different layers, but I found that the workflow bottleneck really hurt my creativity. As a hobbyist, if I'm not having fun, I drift away from the hobby. Professionals want good workflow, since time is money.
The bottom line is if you want to position your players with GigaPulse go for the mondo CPU. If you want all the players to be seated at once, and you want them to be versatile, get lots of RAM. If all you use is a few instruments, and you only need a touch to reverb, go with the best value machine that you can.