Invalid partition table

i have a 250 gig harddrive...partitioned into a 20 gig and a 230 gig...one day when i was jsut screwing around i stupidly did something...and now i get this "INvalid Partition Table" when i boot up...i use windows xp media center edition...any advice will be helpful..

http://www.cgsecurity.org/wiki/TestDisk

let me clarify...i am not able to get to windows in any form..it boots staight to a black screen with "Invalid Partition table" written on it and a blinking underscore

Put in your install disc and go to the recovery console.. try fixmbr and chkdsk I think? There's documentation on Microsoft.com. Might work, sorry to hear about your partition stuff.