I'm gonna rant now!! Coming from Atari St's to Amigas the Mac was my next port of call.
If you are using your computer for design work I'd go for a mac every time, almost every company I deal with use em, every one of them rates them as the best.
If you just want a home computer I would still get a mac, I love mine, but a diy PC would work out cheaper and more flexable in terms of upgrades.
A grand should get you a second hand G5 with plenty of decent software and an apple studio flat screen. I run a mirror G4 twin and a Titanium powerbook and both (touches wood) have been very reliable up to now and trust me they work a full day without giving me a load of abuse.
The laptop has the hardest life travelling everywhere and still works fine where as my dads Crap'ard Bell is only a year old and the screen flops back on it's self and it's only had occasional use; What I'm saying is the build quality on macs is second to non, plus the bonus is they look like works of art compaired to pc's.
Considering my G4 is over 4 years old it hold up very well, some of the designs I work on have a scratch disk size of 1.5gig and my mac handles them really gracefully, it'll free transforms 300dpi in real time without breaking a sweat. I've only ever spent a few quid on ram as far as upgrades and they are solid bit's of kit and are soooo worth the extra investment.
You will also love using osx.