what I mean is what kind of converter should I buy. Or should I just mod it myself?
There are no converters for Xbox to PS3 or PS3 to Xbox 360, at least none that isn’t a waste of money.
Look into doing a Dual-Mod.
You can do one your self or you can find a modder (including myself) here on SRK TT to do the mod for you (for a price)
If you are doing it your self here are the links you need to look at
Dual Modding 101
The Beginners Guide, How To Mod Like a Pro
[*]RJ-45 Multi-Console Cthulhu Arcade Stick Tutorial V.2
Thank you sir.
If you have a 360 TE or a TE-S, you should look into using a TE-Kitty board. It is by far the easiest method to get a dual mod going.