It depends if you are planning on upgrading the processor soon, and if so how soon.
I got a GF4 Ti4200 a couple of months before I upgraded my porocessor/mobo. Buying one of these for a PIII 450 made a difference, well I was going from a VooDoo3 3000, but I only did this because I have since upgraded to an Athlon XP2000+.
If I were you I would save up, and get them all at once, either that or save for a bit and go for a more expensive modern card with the knowledged of a future mobo/processor upgrade.
Going for a MX440 and then upgrading to a top processor, before finding out you want a new graphics card could be slightly wasteful. Unless you want a second system from your "old" parts.
Baz