Several options possible. I also use audigy 2 platinum which includes a breakout box - a panel inserted into a free drive bay, so you can plug straight into a connector. Alternatively you can put a mini jack adapter on your guitar lead and plug into a mic socket on any soundcard.
Software: Several possibilities. Have a look at a copy of 'computer music' magazine or check out their website click here for reviews, tutorials and advice. Their cover disc contains a free music studio called 'muzzys' I believe. I use cubasis vst and music studio deluxe. Both ok. I also use a plug in called amplitude which simulates a variety of amplifiers and effects. Often the basic recorded sound is very flat and dry and adding effects with stomp boxes can add toomuch noise to your recording. Your main problem will
Be aware also of latency issues (a delay in hearing your guitar through headphones/speakers as you record making everything seem out of time with any drums machine/other instruments recorded. This can make multi track recording a nightmare. Look for a soundcard/software that supports ASIO drivers which can combat this problem.
Ideally you will have a reasonable processor and plenty of ram or the recording quality will really suffer.
For info: My system is win xp pro P4 2.6 1GB Ram 2x 80GB Hard drives (Software on 1, recordings on other) Audigy 2 Platinum Cubasis VST 4 Music Studio Deluxe Amplitude Sony CD-RW/DvD RW