Low FPS in CSS with a Celeron 1.7GHz/768MB/9600XT

Hi. Hopefully someone here can help me out. My wifes computer is a celeron 1.7 with 768MBs of RAM and for testing purposes I put my Sapphire Radeon 9600XT 256DDRII into it. Previously she had a PowerColor Radeon 9200SE 128MB DDR.

I just want to know if anyone knows ways of decreasing the workload for her CPU when playing games. Specifically, lately she started playing the game Counter Strike Source, with her 9200SE she was getting 15-30 frames.

With my 9600XT she is still getting 15-30 frames. When bots are added to play against for offline play, the frames drop even more. I found that using the following commands:
r_mmx 0
r_sse 0
r_sse2 0
r_3dnow 0

The frames stay a bit higher because the GPU is doing more work, and the CPU is doing less. I also found that using Task Manager to decrease the CPU priority from Normal to Low also ever so slightly increases the frames, and the frames drop less when adding bots.

Now I was just hoping that someone here would be able to help me out. The CPU cannot be overclocked, how can I take the load off of the CPU so she can play with the highest frames possible. Programs or whatever, Im looking for any ideas.

Thank you.

{EDITE} I just wanted to add that before playing a game, all unneeded processes are closed. Before playing, there are 17 processes running, including Steam. CPU is at 0%. It is CSS that brings it up to 80%/100%.

You can't do much, the 1.7 Celeron is a real bottleneck for a video card like the 9600XT.
Getting a stronger CPU is the only option to get higher frame rates (besides decreasing the ingame graphic detail to the lowest possible level, of course).

Actually the funny thing is that if I have all the in game detail and settings set to the maximum setting, or if I set it all to the lowest, there is not change in my fps. The 9600XT runs in DirectX 9.0, if I run it with 8.1, 7.0, or even 6.0, there is still no change in FPS. Its the CPU that is killing the game, I don't have the money right now to buy her a new CPU and motherboard, I need to make due with what she has. Anyone have any ideas? Possibly to make the GPU do almost all of the work? I mean there must be a program or something.

I started writting one with C++ but Im lost in how to do it. So I gave up. There has to be some sort of program that can do it...