I've found Cakewalk is pretty easy to do the basics on, but it can be a bit tricky when you know what you want it to do, but have no clue how to do it (some of the functions are hidden pretty well). If you're doing this pretty much for fun and not on an important schedule, and really aren't too worried about quality at first, then I'd definitely suggest using Cakewalk or a similar program. Fool around with it for awhile, read up when you can, do some dumb stuff, and then post on the forums whenever you need help with anything. If quality and time are a concern, you're probably better off either buying a multitrack (which is still a pretty big hassle), or buying studio time. If you choose to go with computer recording however, the experience you receive will be great and valuable.
As far as a mixer, you pretty much have 3 options. The first option, and worst, is to basically just plug your mic straight into your sound card. This will only let you use one mic at a time (pretty much impossible if you want to record drums), and will give you very limited control, not to mention leave you with tons of frustrating retakes.
Your second option is to use, as you mentioned, an outside mixer. This will allow you to use more than one mic, and easily control the volumes of tracks, and is a minimum for drum recording. Keep in mind that a "mixer" could be many things, from a multiple input amp with a preamp out to a PA head or simply a conventional mixer. I have both a mixer and a PA head (powered mixer), though I mainly use the PA as it is a lot simpler and more convenient. The downside to this type of recording is that if you are using multiple mics, you will not be able to edit the levels of each mic individually after you record, which can lead to lots of angry rerecords after you discover you recorded your kick way too loud, and it's clogging up your track. Also, with this type of recording, you must record each instrument one at a time.
Your third, and best option (if you have the available funds) is to get a sound card designed for recording. These sound cards will have multiple inputs and allow you to record on separate tracks on your computer. This has many advantages, as you could record multiple instruments at the same time, and also you could edit each line's settings in post. Unfortunately this can be expensive, but most of the time it is a necessity for serious recording.
Hope that helps!
