A good question
 

If I did this, would it be like having a modchip? I mean, could I use the evox bios to skin my xbox, save games to HD and such?

From what it looks like you can, but I only see things about flashing the linux bios.

If you do this it you won't be able to go on Xbox Live at all. Also, it can be alot harder than it looks (depending on your experiance).

yeah, I do want to go on xbl sometime. Guess I wouldnt be able to boot from cd with that way would I?

Well, xbox live has a modchip check (for altered bios). If you flash the TSOP with the hacked bios, you will be banned for sure. Which is why people get modchips, then hook up an on/off switch onto them.