I assume that there's converters about, though it does seem a little pointless. The point of DVI is that you don't have to translate the digital signal to analogue (on the GFX card) and then back from analogue to digital (at the Monitor) again.
Just Digital => Digital ...
Hrm. I'd try to go back to your reseller & try & get an "upgrade" on the GF3 which DOES have DVI - otherwise you'd lose out, I would say.
Hope this helps somewhat. 😀
Sorry - I don't know where/if there are converters, though I do assume so.