Your friend is wrong, not paranoid - there should be no compatability issues - except perhaps with the new 64bit processor, which I would stay away from for now, because of software issues.
Howeever personally I have greater faith in Pentium processors and the long term viability of Intel as a company, anyway. It's an arguable case either way, and some would say it doesn't matter what you choose - but of course you do have to choose, and that won't help.
The P4 2.8GHz C version with the 800Mb system bus, and Dual channel memory, is the "best buy" without going for the more expensive "top of the range" processors from either company - IMHO. In many tests it shows up as faster than more expensive Athlons.
If you don't want to go to this level, then you may find Athlons somewhat cheaper - but it won't be by much either way.
However you also need to concentrate more on video/graphics facilities and hard disk storage for what you want to do.