Pixel8's vga bios, and TATX vga bios are pretty much the same thing, the only difference is TATX allows for more than just xbox v1.0, where as Pixel8's vga bios can only be used on v1.0 xbox's. The tatx bios were built from pixel8s bios.
Higher resolutions are possible with the two vga bios. The problem you are having is your cable. You have to have an HD cable, or set the right pin settings for HD, to access 720p and 1080i in the ms dashboard. If you set pin 11 to 9, the cable will go into vga mode (GOG), and only 480p will be possible; 720p and 1080i will not even show up as an option in the ms dash. I am using a modified HD cable, and I get 720p and 1080i with the vga bios.
The only problem with the higher res settings is there is a color ratio imbalance; too much red and not enough blue in the picture. Making playing games in 720p or 1080i useless. Some monitors will display the color ratios correctly, but a lot of monitors don't work correctly in 720p and 1080i due to the syncs used in the higher modes. Basically in 480p the sync pulse in the video is "bi-level" meaning it only goes negative and the vga bios is designed to "clip" that negative sync off. 720p and 1080i use a "tri-level" sync meaning the sync goes negative and then positive. The vga bios are only able to clip the negative portion off but can not do anything about the positive portion of the video. A lot monitors will interpret this positive sync tip as color info and sample the black reference level incorrectly. I expect there may be a way to fix that with the VGA BIOS if it is designed to switch the video encoder to use "bi-level" syncs for those video modes.
The other main problem, as you have stated, is a lot of good xbox games, including the n64 emu's, turn green after the initial boot.
Another problem with the vga bios is that it does not allow support for the Lba48 hack; allowing for hdd's greater than 137gb. When this hack is implemented, and the vga bios are on, nothing on the f or g drives will be recognized.
The vga bios have been in the beta stage for almost 2 yrs now, and nothing has been done on them since (I assume the author, Pixel8 has lost interest in his project). This really a shame, because the games the vga bios do work on look and work amazing. There are a quite a few people who are interested in this; hell, it would alleviate the need to buy an expensive transcoder for the xbox, and give a better truer vga picture. This topic is discussed extensively in the video/audio section, here on xbox-scene, and on xboxhacker.net, for those of you who would like to learn more on the subject.
EDIT: Also, i could care less about the vga bios being 256k, for one, they more than likely will never be because they are based off the 512k dubug bios, and another, what in the hell did you get a 256k chip for?