Start out just using the line input on your Mac, if your Powerbook has one, and the software of your choice. A very cheap and limited but nonetheless useful software option is GarageBand which comes with iLife. It only allows recording of one track (mono or stereo) at a time, but has some nice built-in FX and softsynths, and supports audio, MIDI, and loops. Great for the first-time home studio, and you can always upgrade to a better DAW if you need the features.
You'll need mike preamps, which you can get built into a little mixer like a Behringer UB802 ($60). (Don't go smaller than that, the 502 doesn't have phantom power.) Another option is an M-Audio "Audio Buddy" dual-preamp for $80. But I find it's handy to have a mixer in the studio (I have 5 because I buy 'em but never sell 'em, even the one I got in 1978. They all get used.)
You'd plug your synth and mike into the mixer, and plug the stereo outputs of the mixer into your Line In jack using a cable you can get at Radio Shack (1/8" stereo on one end, two RCA plugs on the other).
Are you only going to be recording yourself, or will you be recording other peoples' work, or will you have other folks sit in and do tracks for you?
My favorite starter mike is a
Shure SM58 ($100) for vocals, or SM57 ($90) for instruments -- and you can use either for either. They're the same mike, but the 58 has a pop-filter (ball head) for vocals. More hit records have been made with these industry workhorses than probably all the others put together. However, many people prefer the sound of their voice or instruments using a condenser mike. Good examples of these include
the Rode NT1-A (about $200) and Studio Projects B3 (about $165). These are on-line prices, but it makes sense to go to your local pro shop and try them out -- well worth the extra bucks to get the one that suits you.
Don't skimp on mike cables. The really cheap ones have bad "microphonics", meaning they add loud sounds to the signal when they bump against something, and pick up noise from the floor. Trust your pro shop for a normal decent cable, nothing fancy required.
Lots of folks spend hours discussing the subtleties in differences in sounds for different soundcards, preamps, mikes, and the lot. However, what I find is that the simplest decent equipment, like the above mentioned, is by far good enough to do very good work and learn the craft of recording and mixing using a digital studio. The experience and talent of the engineer make a lot more difference than the equipment, until you get pretty proficient. So, unless cost is no object, start out with simple but decent gear, and learn as you go. Find out what you are able to do with the simple stuff, and learn its limitations (while expanding your own limits). Once you've recorded at least a CD's worth of material with the simple gear, you'll have a better appreciation for what better gear has to offer, and you'll understand the tradeoffs better.
I don't recommend partitioning; all it will do is leave you less space to play with -- more constraints. Partitions are nice if you need to reload your OS but keep your data, though. It won't help the performance of a DAW, actually it's more likely to hurt it. Until you get into lots of tracks you shouldn't have a disk drive performance problem anyway, and if you do, you'd want to get an external firewire hard drive. But I've never needed one for my laptop.
The line inputs on your computer are limited to 16-bit recording. You can do just fine, but when you step up to 24-bit recording you'll understand the benefits, and in the meantime, while you're discussing the pros and cons of different interfaces, you'll be spending MORE time learning to arrange your songs for recording, recording, and mixing.
HTH
