First PC or first computer. If the latter then that would be the Acorn Atom, the precursor to the BBC Micro. It had 1KB of RAM, which my dad slowly upgraded 1KB at a time as memory was expensive. Unfortunately he blew something up once he reached 7KB.
First actual PC, again technically my dad's, was an IBM PS/2 Model 50 that he acquired from work: System specs:
CPU: Intel 80286 10MHz
Memory: 640kb
Hard disc: 20MB
Floppy disc: 2x 1.44MB 3.5"
Graphics: VGA (640x480 in 16 colours or 320x200 in 256 colours)
Sound: PC Speaker
Expansion ports: 3 MCA slots, 4 ISA slots
Keyboard and mouse: PS2 (duh)
Monitor: 12" black&white VGA monitor.
OS: IBM DOS 3.something
I mostly used it to play the original 2D Duke Nukem
First PC that was actually mine was an Amstrad PC7486slc/33. This was a particularly nasty bit of kit from Amstrad, it was actually a 386 based system with one of those Cyrix 386->486 upgrade CPUs that never quite worked right. It used to crash trying to play Heretic if you didn't run it with -debug. This is because it had a 386sx motherboard, complete with only a 16bit wide bus, but would accept a 486 instruction set that was designed for a 32bit bus.
CPU: 486slc 33MHz
RAM: 4MB (4x 1MB 30pin SIMMs)
Maximum RAM: 16MB (4x4MB)
Hard disc: 200MB
Floppy disc: 1.44MB 3.5"
Graphics: Cirrus Logic SVGA w/ 1MB video memory (max 1024x768 256 colours, 800x600 16 bit colour or 640x480 24bit colour)
Sound: Soundblaster 8bit ISA card (mono) hooked up to a guitar amp
Expansion ports: 2x ISA
Monitor: 14" Maximum res: 1024x768 @ 30hz interlaced or 800x600 @ 60hz
OS: MS DOS 6.2 + Windows 3.1
Mostly used to play Doom
