hdd size and ram won't give you even 1 fps extra.

ET needs few ram it's a 2003 game, it needs less than 512mb of ram, maybe around 300mb, so you can play even with 1gb total, depending on how much ram your operating system and other software use. You have 2gb so np 4 you. Don't just listen to what people say, open et and check how much ram it uses, whoever says ram doesn't have a clue.
As regards a bigger hdd, I don't see how you can get more fps with that, once you load the game and the map it's loaded lol.

What imho counts is cpu speed (ghz) (et is not multithreaded, and it doesn't run on more than 1 core! So don't bother about having one trillion cores, the only advantage would be that other processes can run there, but as for et, no gain from that) and maybe graphics card.

I'd say not much graphics card, I have a radeon hd5670 which is certainly not a top one, gpuz gives me a peak gpu load of 33% while benchmarking an et demo with /timedemo 1, that is, with the game running as fast as possible and not normally, like when you play. That gives you an idea about how much I use my graphics card when I play. Generally not even 1 third of the gpu power is used. My bottleneck is just the cpu ghz (I have less ghz than you -.-).

So, to summarize:
- keep your ram, and hd, and cpu
- buy any cheap graphics card
- play et and have fun :p

edit:
I use Win Xp (for tzac servers) and Linux (for all the others), I don't know how much ram wincrap7 needs to run but I suppose 2gb is still ok