First PC, 286 with 1 meg ram and 20 meg HD
, first computer, ZX81 (1 kilobyte of RAM, no internal storage, B&W screen touchpad for a keyboard) which I still have. I actually had 2 games published for it when I was 12.
a brief guide is
Games - plenty of Hard Disk space - fast Gfx card with loads of GFX onboard memory(not shared memory!) - CPU and core memory need to be reasonable not not ultimate
Video editing - Absolutely loads of disk space ( more than 300 gig realistically), fast CPU and loads of RAM.
Photo editing, lots of RAM and a good CPU, disk space you will need moderate especially if you capture in RAW mode (my new camera produces 12 Meg images, these soon add up!)
Musician, - moderate spec PC with the best soundcard you can buy will be fine
As Kipax has said, todays lowest spec PC is an order of magnitude better than you need for Office/internet work. Todays £400 PC has probably 1000x more power than NASA had when they put a man on the moon.