Sirestap: I have the Xbit solderless chiip. It rocks. Although I may solder it anyway because occasionally it slips and I have to kick the machine a couple of times to get it to boot
And here's how to do the Splinter Cell hack:
Before attempting it, read EVERYTHING, and then go to the other tutorials and read lots of those too. One boo-boo and goodbye Xbox.
And in case anyone has worries about content of the post, currently it is not illegal to mod your box. Distribution of mod chips with a copy of a hacked bios is indeed illegal, but softmodding (using save games) or selling chips with no BIOS violates no laws.
Obviously using these techniques or tools to pirate games is illegal, but there is also a large homebrew community making some incredible tools for the Xbox. The media player for one is an indispensable tool.