I was in your same position last October, when I was finally able to really afford a computer I really wanted. I had wanted a Mac for several years, but had to use Windows. Windows was OKAY, but it seemed everytime I had something important to do, it would give up on me! After a lot of research and putting quite a bit of thought into it, I finally decided to gamble on a Mac, and let me tell you, it was the best PC related move I have ever made.
I'm currently in college so I mostly use it for my online classes and word processing. I also have quite a bit of music, among other things. The only thing I have to use my HP for is the discs that came with my books that have to be installed, as they only run on Windows. I recently bought SimCity 4 and it runs great on my iMac. The only problem with that is that it has very limited support from EA, which of course is no fault of Apple. The best thing about switching is that I am just so much more productive now. At first it did take a bit of getting used to, as some things you just do differently on a Mac, but I was expecting this. To this date I haven't gotten any error messages that are completely random and make no sense, like I used to get continuously on Windows. I got an 20" iMac Core 2 Duo with 2GB of ram, a 500GB hard drive, a 256MB ATi graphics card, with a 3 year extended warranty and Microsoft Office (student edition) for under $2,200 (with my student discount) and it was most definitely worth every penny.
With Windows based PCs I actually prefer HP because I have had a totally different experience with their tech support than Chicken Mania. With that being said, if you do go with an HP be sure and get a higher end model and NOT a Compaq, as they are continuously troublesome. HPs do tend to have hard drive failures quite often though, so beware.
The decision is ultimately up to you though, and no one can make it for you.