Yep, should be Ok. I found that DDR massively improved performance on my system. The HDD doesn't really need to be that big if it only has CS and Steam on it, so you could save a bit of cash there.
RAM-wise it looks ok, and the CPU will probably be fine because HL needs a minimum of a 266, lol.
Are you planning to have bots playing as well? This will affect server performance.