Honestly, that rig is gonna stutter no matter what you slap into that PCI slot :-/
Bliz did a poor job on its estimated system req's, as thousands have complained about since its release. I really think a 1.2 gig processor and a gf3/Radeon 7500 should be the bare minimum to play this game.
I've run WC3 since legit beta, and had an AXP 1800+ and a gf3 ti200 OC'd. It ran very well with maxed out everything at 1600x1280x32. Now, most people are saying thats the extreme resolution, but honestly, the game looks pretty crappy at anything other than maxed out rez and details. I just slapped in an Albatron ti4200 Turbo and didn't even realize how much the game stuttered before. Whether it was scrolling or a massive bloodlusted battle, the game would lag some on my gf3, but it runs without a hitch now.
Now those of you who have played WC3 know how important it is to have good frame rate in a huge battle like that...you simply can't micro if you aren't getting consistent, high frame rate. I would go with the best possible PCI card around, the Radeon 9000, otherwise your friend may want to consider a full system upgrade. I'm pretty sure WC3 is gpu intensive rather than CPU intensive, but thats just my guess as I haven't seen it on anything other than my AXP at 1.7 gigs. But judging from the very significant increase in performance I saw when I switched from a gf3 to a gf4, I think its the GPU thats the bottle-neck.
Chiz