He said he is more comfortable with playing at a lower resolution. Most likely because he has been playing with it for a long time.
I have played Counter-Strike 1.6 competitively, and many people worry about resolution. I have yet to see a top competitive CS/CSS player use a resolution larger than 1024x768. I use the lower resolutions too just because I seem to register better (although it might be "just in my head.") and I can maintain constant 100fps on any resolution.
Now to answer the OP's question: Do you have an NVIDIA or ATI graphic card
? If you do have a NVIDIA card, you can go into your NVIDIA Control Panel. Then on the left side click "Adjust desktop size and position." Then select one of the options:
Use NVIDIA scaling: This MIGHT remove the black bars (never tested this)
Use NVIDIA scaling with fixed-aspect ratio: This will add black bars in order to maintain proper aspect-ratio
Use my displays' built-in scaling: This removes black bars and stretches your screen to match your monitor
Do not scale: This SHOULD be the same as above
NOTE: I only found these to work in XP. In Windows 7, it seems to automatically go to "Use my display's built-in scaling," and has black bars by default. You can give it a try to see if it works. I don't think the NVIDIA drivers are perfected for Windows 7, hence why the scaling options seem to be glitchy.
ANOTHER NOTE: I play with the black bars. I think all or most of the "top caliber" gamers play with black bars if they have a widescreen monitor. I THINK the stretched screen (4:3 resolution on a 16:10 monitor) makes the left and right sensitivity slower than the up and down sensitivity when moving with the mouse. I would recommend playing with the black bars (only when playing CS/CSS of course if you want to use the 800x600 resolution.)