You might want to try an extra 256Mb stick of RAM, I was running XP with 256 and it used to chug a fair bit. RAM is dirt cheap at the moment so cost shouldn't be a big issue. Although I don't think you will see a big perfomance increase in MOH.
I'd be pretty happy if I was getting those kind of frame rates.
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Lady Astor: "Winston, if I were your wife I'd put poison in your coffee."
Winston Churchill: "Nancy, if I were your husband I'd drink it."