whould this do hl2 well

AMD Athlon XP-64 2800+ (1800MHz) 1600MHz512kb S754 Boxed Gigabyte GA-K8VT800 DDR S754 VIA K8T800 LAN/SATA
DDR 512 MB - 400 PC3200
Sapphire ATLANTIS RADEON 9600XT, 256

if not what whould

My suggestion would be to bump the video card up to a 9800 Pro 128 Meg, or maybe even a 6800np.
There's not much point in buying a 256 Meg 9600XT as it's not fast enough to take advantage of the extra memory.

and what whoud be the oc capabilitys

i would also try to get 1gb of ram, when i play cs:source, my ram usage jumps from like 350-750ish.
I've heard some ppl have had performance improvements after getting 1gb. I would also get a better graphics card

i'm thinking of upgrading my system in a similar fashion:

A64 3000+
Chaintech VNF-250
512mb DDR3200

and using my plain jane 9600...

now i don't need to play HL2 @ 1600x1200 or anything, i'm just looking to do 1024x768 w/ medium features enabled...

my current system:

XP 1700+ stock
nforce1 mobo
512mb PC2100
r9600 np

does Far Cry @ 1024x768 w/ medium + low settings, so i was thinking the CPU/MOBO/RAM upgrade would boost the performance significantly...

and i could always buy a 6800 or something next year when it becomes necessary for the new games or something....