I have a qtek s100 rom buymobiles.net or something like that.
I used the program to hack your own rom for Extended storage - made a safe backup first to keep on my PC, just in case, hacked the ROM, flashed it back on the phone and it worked fine. There are a number of error messages that come up, but they're all to be expected, but do follow the instructions carefully and they'll put your mind at ease.
After the flash, you get 27mb of "Storage" instead of the previous 7mb. I've got a 1gig card so it doesn't make much difference to me, but it's useful, and worth doing at the start so you don't have to re-install everything if you do bite the bullet later and apply the hacked ROM.
The hacked ROM will be a copy of your own ROM, so nothing will change ROMwise, however, I foolishly overlooked the fact that that space comes from somewhere, in this case it wipes out the intellidialer and some other gubbins. I had no backup of these, but forunately it's all stored away on the XDA developers FTP. Someone more informed than I can correct me, but I think the only files you really need to reinstall are the intellidialer. Also squirrel out the cab that contains settings for your network, orange, O2 etc (i haven't found these, they're on XDA developers somewhere bu i forgot where! Drop me a line if you find them...)
Once you've done that - well, your phone is pretty much as it originally was, but with a bit more storage for free. not a bad thing.
I would flash the ROM and then reinstall rather than doing a Sprite Backup/Restore, since the registry will be in a very different state after the ROM flash. However, i don't think it'll do any harm.
Sprite Backup is certainly worth getting hold of, and keep a copy of your backup on an SD card and your PC in case your phone gets 'half inched'.
Hope that helps.