I only liked the begining part of Sandtraps, all the way till the jumping from rock to rock, can get a bit tedious after sometime. Some parts of Ravenholm were pretty boring too. The ending part was the best (from where u finally meet the monk and till you exit the mines to the garage)
His specs should be good enough to last until end of next year so theres no use upgrading now. Im running on a XP2600 2.14 GHz with a 256MB 9600XT and 768MB RAM. Thats way lower than his and i can already run HL2 and CS:S maxed out.
The cremator head is still in the game, in eli's lab, its the jar on the table right behind mossman when eli is talking to you. When you go to the head in the jar, eli would say "Alyx brings in the weirdest things"
I think most morden video cards starting from the GeForce FX family to the Radeon 9500/9550/9700/9600/9800 family, GeForce 6 family and to all the Radeon X300 and above family