Speaking as a person who's gone both routes professionally, I'd say it depends on your long-term goals. If you want to be able to take your projects to larger studios to mix, or if you plan on working as a freelance engineer, or as an on-staff engineer at a recording studio, I recommend learning Pro Tools as soon and as well as you can. If that's not a big deal to you, or if you don't see yourself really moving out of a home-studio environment, then the benefits of learning Pro Tools are greatly reduced.
Basically, with Pro Tools, you're paying a premium for no reason other than being able to use Pro Tools. Almost any other program (Reaper, Sonar, Cubase, Digital Performer, etc.) will let you use whatever hardware you like, whatever plugins you like, and will most likely have more features than Pro Tools. Pro Tools locks you in to Digidesign-approved hardware (not many choices) and Digidesign-approved plugins. The main advantage of using Pro Tools comes into play when you get one of their HD systems, as they have onboard effects processing which takes almost all of the processor load off of your computer. This is why you see professional studios running 48+ channels of audio with tons of effects, on an old G3 or G4 mac. Consumer/pro-sumer systems like the Digi002/003, M-Box, etc. don't have any onboard processing power, and thus don't really give you any advantage whatsoever over non-Pro Tools compatible hardware.
On the computer side of things, a well-built PC will work just fine with Reaper/whatever program you choose, but make sure to read up as much as you can on hardware/software compatibility issues and whatnot, as many times things like what chipset your motherboard uses, or what version of what drivers you use for stuff, makes a huge difference in stability. This is a large reason why many people prefer mac's over Windows-based PC's: stability. Yes, you *can* create an incredibly fast, stable, and relatively inexpensive PC that will work for you for years and years without issue, but it simply takes more work/research/maintenance than a similarly-configured mac. This is coming from a guy who's built/repaired his own PC's for 10+ years. I just went the Pro Tools route with a MacBook Pro and, while I miss some things about Sonar, I definitely don't miss a single thing about my PC except for it's gaming capabilities (which I don't really care about as I work so much I don't really have time for gaming anyway

Except for the odd Diablo 2 session here or there hah)
When it comes to Mac Mini's, be sure to get the higher-end one. The ones with the smaller amount of ram are SEVERELY limited. Recording programs take a lot of resources, and you don't want to be limited right off the bat by the amount of memory you have. Get something with at least 1 GigaByte of memory, preferably 2GB if you can afford it. A large external Firewire drive is also a must!
Hope this helps
