First one I bought myself was a custom built Pentium 4, before that they were all hand-me-down 486s, a Pentium MMX and a Duron. The year was 2003 and I built it the summer after doing my GCSEs.
I remember being really pleased because the Processor was the best I could get at the time, with a decent motherboard etc and 512MB RAM (back when that was a lot!

) I still use the case for my spare PC
Specs:
Intel Pentium 4 - 3.06Ghz 533Mhz FSB CPU with Hyperthreading (had to turn it off in bios to start with due to compatibility issues, helped later on though)
512MB RAM 333Mhz DDR PC2700 - Samsung
ATI Rage Pro 128MB Graphics Card (had numerous driver issues, which put me off ATI for years, ended up burning itself out)
V700 Case with Generic 350W PSU, which ran fine for 10 years until I threw it out
120GB Maxtor HDD, has just gone faulty 10 years later with SMART failure
Zalman CPU Cooler
16x CD-ReWriter + DVD ROM/CD-rewriter Combo 4x, from my Duron
Floppy Drive.
Cost about £800 I think in total...
Was a nice computer, ran Windows XP and was very quick at the time. My sister was using it minus it's case (with some rubbish £10 job) until last year when I yupgraded it with parts from the MM to a Core 2 Duo, due to it being far too slow with Windows 7. It had 2GB RAM by then but had grown slow with age. It did well though!
Someone on these forums bought it off me for a tenner (the mobo, original ram and CPU)...