1) You can lay multiple tracks the easy way or the hard way

The easy way will cost you about $35 but is well worth it. Go to
www.fasoft.com and check out n-Track Studio. There's even a forum here for it! The shareware version is workable so you can see whether it'll work for you. The HARD way to record multiple tracks is to use the "single track" software you already have. This sucks big time and I wouldn't bother with it when n-Track is cheap and is supposedly as good as the big dogs (I've never tried the expensive software and have no desire to now)
2) You don't want to plug your mic directly into your soundcard. First of all your soundcard probably won't like it too much. In fact I've never had a soundcard that worked with dynamic microphones. Besides, the Mic-in channel on most soundcards is MUCH noisier than the Line-in channel.
What you'll need to do is use a preamp on your mic and then run the preamp into the Line-In port on your soundcard. Deselect all the other input channels via your soundcard's level properties (click the speaker in the taskbar). I'd say that most anything would work as a preamp. I use my old Fostex 4-track which works real nice. Be sure to be careful that you don't blow your card though...you don't want to amplify your mic THAT much
Sounds to me like your computer has the processing power and memory to handle recording (assuming you have an Intel processor..PII or Celeron). The thing that *might* slow you down is the hard drive...not you can do with a laptop ($$). You also might find out that your soundcard is really noisy too, and there's not much you can do about that either.
If you really want to get into recording and want a versitile setup then trade your laptop in for a desktop machine. You can probably get an even trade on a faster desktop! (yes I know that in some cases laptops are necessary, it was just a suggestion)
Slackmaster 2000