Check you buy a 3000+ / 3200+ that does not require DDR400 tho - there is an XP3000+ and 3200+ that runs the 333 / 166 RAM that you have now.
Alternatively look for a 2500+ Barton and overclock it ... RAM speed could be an issue though, and DDR1 is getting expensive now.
From wiki - the Bartons have a 512K cache and are a tad better at gaming due to it.
[edit] Athlon XP "Barton" (Model 10, 130 nm)
CPU-ID: 6-A-0
All models support: MMX, SSE, Enhanced 3DNow!
Model Number Frequency L2-Cache FSB Multiplier Voltage TDP Release Date Part Number
Athlon XP 2500+ 1833 MHz 512 KB 333 MT/s 11x 1.65 V 68.3 W February 10, 2003 AXDA2500DKV4D
Athlon XP 2500+[4] 1867 MHz 512 KB 266 MT/s 14x 1.65 V 68.3 W December 2004 AXDA2500DKV4C
Athlon XP 2600+ 1917 MHz 512 KB 333 MT/s 11.5x 1.65 V 68.3 W September 21, 2003 AXDA2600DKV4D
Athlon XP 2600+[4] 2000 MHz 512 KB 266 MT/s 15x 1.65 V 68.3 W December 2004 AXDA2600DKV4C
Athlon XP 2600+[4] 1900 MHz 512 KB 400 MT/s 9.5x 1.65 V 68.3 W ? AXDA2600DKV4E
Athlon XP 2800+ 2083 MHz 512 KB 333 MT/s 12.5x 1.65 V 68.3 W February 10, 2003 AXDA2800DKV4D
Athlon XP 2800+[4] 2133 MHz 512 KB 266 MT/s 16x 1.65 V 68.3 W December 2004 AXDA2800DKV4C
Athlon XP 2900+[2][5] 2000 MHz 512 KB 400 MT/s 10.0x 1.65 V 68.3 W December 2004 AXDA2900DKV4E
Athlon XP 3000+ 2100 MHz 512 KB 400 MT/s 10.5x 1.65 V 68.3 W May 13, 2003 AXDA3000DKV4E
Athlon XP 3000+ 2167 MHz 512 KB 333 MT/s 13x 1.65 V 74.3 W February 10, 2003 AXDA3000DKV4D
Athlon XP 3200+ 2200 MHz 512 KB 400 MT/s 11x 1.65 V 76.8 W May 13, 2003 AXDA3200DKV4E
Athlon XP 3200+[3] 2333 MHz 512 KB 333 MT/s 14x 1.65 V 79.2 W October 2003 AXDA3200DKV4D
Get a second hand one (your choice) for a few bucks and it will give you a bit of a boost but a complete system rebuild is required for tackling the latest games at a decent res.
I have a 2400+ running a 6800Ultra AGP and it runs most of the games at low res - running it at 2Ghz - it isn't a Barton.
Going from 1.8 to 2.2Ghz should show an appreciable gain - with the double sized cache from a Barton chip about another 10% gain too.
If your strapped for cash and can get something for a few bucks it will help.
Just don't expect miracles.
An aftermarket cooler will help greatly as these chips ran damned hot - 80 watts there abouts under load.
Don't waste any more money beyond this - try to overclock the one you have for a lark perhaps?