I have same system as you sort of, but man my results are different:
AMD Athlon Thunderbird 1.333 ( put a slight overclock on it tp 1.40)
128 meg of system ram
winxp
Geforce Fx 5200 128 meg (pulled from a brand new Dell I don't know who really makes it) Mine didnt have a fan either (great heatsink though) I slapped one on for the heck of it.
Letting Windows "auto detect" (a) my clock etc of video card I am set at Core clock of 306 MHz and a Memory Clock of 514 MHz I also left the slider set far right for "Quality" at this point.
Running Default details in game, made sure by hitting "Default" video settimgs are 1024 x 768 512 and Unlimited
All the boxes are check on (Bump mapping etc.)
Played game for an hour or so just now. Turn fight with a Spitfire in a P51B (which I won btw

) I was mid 70's fps whole time. Big furballs I drop to the 50's and 60's. Flying without anyone real close otw to action im 80's and 90's. Looking striaght up is slightly over 200 fps. In tower F4 external view without clipboard if 52 fps. Darn good for a card the "experts" dump on so much as being "not any good".
Im pleased as can be, this isn't a high performance box - and a slightly better than bottom line video card (they are round 50 some odd bucks at newegg). I'm not even going to fool with a formal overclock, it is running great.
(btw I am running the Omega drivers - forgot to mention that)
(a) Display Properties, "Advanced" Tab, "Geforce 5200" button, "Clock Speed" option, "performance" pull down selection, (check load at startup box), then finally "auto Detect and let Windows figure out the settings - takes couple of minutes be patient.