Well, you have nVidia 7100 which is old and it runs on 64-bit memory interface (it's the memory speed, which is quite low).
But have you done following in console?
fps_max 300 (or 100/200).
cl_updaterate 100
cl_cmdrate 100
rate 25000
You have lowered the resolution and graphics ingame?
And remember to deactivate Blooming in options, also Anti Aliasing.
Found some on Google:
You will need to make a file in "counter-strike source/cstrike/cfg/" named autoexec.cfg. Open this file with notepad or whatever and add these commands:
r_3dsky 0
turns off some of the 3d objects looming in the sky. This is currently considered a cheat for unknown reasons, thus will only work in your servers until its fixed. Major fps boost. Little gfx loss
r_shadows 0
One thing im sad to say is....shadows in HL2 suck. Well at least in CSS. Until they fix this, itll look better without em. Major fps boost. Little gfx improvement
cl_smooth 0
Not much is known about this command except that it lowers fps when enabled(which is default). Ive played with this on and off and theres no gfx difference at all. Moderate FPS boost. No gfx loss.
cl_phys_props_enable 0
BIG help! This removes the smaller junk items that choke your cpu for processing. Items like tires, barrels, crates, and all the important stuff stay. Huge fps improvement. Less clutter.
GL HF