[Fried Chicken Boy]

4GB of RAM should be fine for your OS to record audio. You might try a Beta release of Audacity. In the notes on the website, the developers are saying that the stable release can be buggy in Vista and 7. As it's free, can't hurt to give it a try. Just make sure you do a clean install.

I would also recommend Reaper; very solid but also more complex (read: bells and whistles). Completely free and uncrippled to try, US$60 to buy a non-commercial license. If you don't mind a nag-screen, I think you can keep using it beyond the trial period for free.

Regarding soundcards, I don't know what you're budget is and Turtle Beach and SoundBlaster are certainly good cards but I would recommend the M-Audio 2496. It's an entry-level pro audio card and the sound quality is superior to virtually anything close to that price range (right now about US$90; not sure what that transfers to in GBP). Only drawback is that it's strictly stereo if that matters to you; no 5.1 or 7.1 surround with this thing.

Btw, +1 for Adobe Audition. I've been using it since it was Cool Edit Pro (some 10+ years ago) and still get great results but you're gonna pay for it (US$300-350). There were a couple bugs with it in Vista and 7 but Adobe released a patch not long ago that seemed to take care of most of the issues.