I like to play an old DOS game once in a while:
In that case forget ATI, cause their VESA compatibitlity
is horrible. (tested radeon 9200/9600)
Nvidia cards tend to have very good VESA 3.0 support.
next I dislike noisy fans on graphics cards.
So personally, for that Pentum450, I'd get a Geforce MX440.

Thanks on the comments re: the VESA support of ATI...I've been trying to decide between a Radeon 9250 and FX5700LE and that pretty much settles it.

Incidentally, the Linux support for earlier Radeons is far better than for nVidia; see http://dri.sourceforge.net/cgi-bin/moin.cgi/ATIRadeon (which is why the 9250 was tempting).

On a slightly better machine, I had good experience with a geforce 4 mx.

Used it both for windows 98 / me / NT / XP and for native dos games. Didn't use DOSBox back then.

I would highly disrecommend an MX card, since they are the super-cheap budget-line GeForce2 rebrands. Get an FX5200 if you need something with stock passive cooling; it's faster, has more features, and will run you only a marginally higher cost.