Much trouble has been caused by the fact that while Mac ROMs can be made to run on the quite-desirable nVidia 6 and 7 series, whenever some hardware differences, even subtle ones, exist, a ROM that runs perfectly well on one card may simply flop on another. This is especially true with 6200 and 6600 cards, where manufacturers, eager to market these "low-to-midrange" cards at minimum cost, employ a variety of ever-changing board designs and memory configurations. This often means a long time spent testing and perfecting a ROM for each particular brand, model, and revision of card.
For quite some time, no ROMs were released for these cards. Now, you will be seeing more 6 and 7 series ROMs available; some immediately, some very soon. An effort will be made to release a few ready-to-flash ROMs for common PC card models, but most importantly, guides are being constructed to allow you, the would-be flasher, to create your own custom Mac ROM, based in information held in your card's PC ROM.
As always, members of the The Mac Elite Forum are available to offer advice and assistance, but we won't write your ROMs for you. We will, however, make an effort to provide all the tools necessary for anyone to do the job themselves.