I know this doesn't answer your question exactly, but I had a PII400 with a voodoo3 3000 in it and it scored 550 in 3Dmark2k1. New games weren't running well if they would run at all.
I put a GeForce2 Pro in it and my 3dmark2k1 score tripled. In otherwords, you'll get an improvement with your PIII 450, but it will bottleneck since this same card can pull off an additional 3000 points on a new system.
You're in a situation where you really need both a new CPU and videocard to get great performance, but at the same time you're not really playing any new games. A new videocard will make it "better", but you'll have to decide how new of a card you want. I would base your decision on when you plan on upgrading the CPU. If you're not planning on an upgrade soon I wouldn't get anything beyond a GF2.
<font color=red>God</font color=red> <font color=blue>Bless</font color=blue> <font color=red>America!</font color=red>