I've been using windows PC's for 7 years to record with... I'm not a professional, I just do it for myself but I have good results and the results are getting better all the time. I remember when I first started recording on Windows I would get errors all the time up until XP and now I can do 28+ tracks on my el-cheap-o Emachine laptop with a 64bit AMD 3200+, I just upgraded the hard drive to a 7200rpm hard drive and made sure I had at least 512mb or RAM. I also use a USB sound card for my audio recording, or my buddies Tascam us-428.
I have a friend that owns a small studio and has been using the same computer since 2000, a Pentium III 833mhz processor running Pro-Tools and a Digi-design multi channel audio card. He records comercials for local and semi-local companies, records phone "on-hold" messages, music for Video games and B-movies and makes a living on his recording and weekend gigs.
If you plan on going professional, a Mac would probably be a good way to go ... but if you're going semi pro of personal use only, a PC laptop will do just fine. Just make sure you set it up for high performance Audio:
* 7200 rpm hard drive
* lots of Ram (512 or higher)
* P4 2.5 ghz or higher or
* AMD 64 bit 2800+ or higher or
* AMD Athlon XP 2800+ or higher
* Windows XP (Pro would be best)
* External USB or Firewire audio card
* A good recording software (Pro tools, Cakewalk Sonar 5, ect...).
* Good mastering software (Wavelab 5.0)
* CD/DVD burner to back up your data.
* Most "gamer" laptops would be perfect, like Alienware.
There's a good starting place.