Re read what Mr Sound said. MIC the amp, run the mics into the Mackie, then run the Mackie into your soundcard.
What kind of soundcard do you have? What all do you plan on recording? If you're just going to be recording your guitar and maybe some vocals or keys, I suggest getting a pre amp.
The Mackie is a just collection of preamps, that aren't all that great, it's the number of them that justifies the cost. Getting 2 DBX or ART pre's will sound worlds better.
The M Audio Audiophile is a good entry level soundcard. The difference between the cheapo A/D converters and expensive converters is like the difference between an RX 20 and a JEM.
However, if you're looking to record full on drum kits, you'll need more channels, and a soundcard that has 8 ins.
What do you have for microphones? Do you have real monitors? Do you have a dedicated control room?