I looked at this a little more - 855wrap will not work with tc (no error messages, but the colours are not correct), but it works with dsl on the same machine.
915resolution will not work for me either, even though it appears to recognise the chipset: $ sudo 915resolution -l
Intel 800/900 Series VBIOS Hack : version 0.5.3
Chipset: 855GM
BIOS: TYPE 2
Mode Table Offset: $C0000 + $36f
Mode Table Entries: 21
Mode 30 : 640x480, 8 bits/pixel
Mode 32 : 800x600, 8 bits/pixel
Mode 34 : 1024x768, 8 bits/pixel
Mode 38 : 1280x1024, 8 bits/pixel
Mode 3a : 1600x1200, 8 bits/pixel
Mode 3c : 1920x1440, 8 bits/pixel
Mode 41 : 640x480, 16 bits/pixel
Mode 43 : 800x600, 16 bits/pixel
Mode 45 : 1024x768, 16 bits/pixel
Mode 49 : 1280x1024, 16 bits/pixel
Mode 4b : 1600x1200, 16 bits/pixel
Mode 4d : 1920x1440, 16 bits/pixel
Mode 50 : 640x480, 32 bits/pixel
Mode 52 : 800x600, 32 bits/pixel
Mode 54 : 1024x768, 32 bits/pixel
Mode 58 : 1280x1024, 32 bits/pixel
Mode 5a : 1600x1200, 32 bits/pixel
Mode 5c : 1920x1440, 32 bits/pixel
Mode 7c : 1024x600, 8 bits/pixel
Mode 7d : 1024x600, 16 bits/pixel
Mode 7e : 1024x600, 32 bits/pixel
$ sudo 915resolution mode 1024x768 16
Intel 800/900 Series VBIOS Hack : version 0.5.3
Chipset: 855GM
BIOS: TYPE 2
Mode Table Offset: $C0000 + $36f
Mode Table Entries: 21
I noticed a while back that xsetup.sh will only list 640x480x16 in tc whereas in dsl it listed several modes - maybe linux-2.6.26 is being too clever for itself and restricting things to the screen resolutions it can use with the video memory it believes is available?
Edit: after checking the readme, it appears you can try to replace an existing mode - "sudo 915resolution 30 1024 768 16" doesn't seem to work either...