Navvid, to get the spacing right, you could try one of these:

http://www.stewmac.com/cgi-bin/hazel...talog/sku.html

Additionally, your string slots really need to be rounded at the bottom, as opposed to the V slot you're going to get if you use a regular file to make the slots, to properly seat the strings, and avoid problems with string breakage, wear, intonation, tuning and such. Stewmac also sells nut files which leave a proper, rounded seat for the strings. Now, if you want to get the whole thing, they sell an essential nut making kit which has everything you need:

http://www.stewmac.com/shop/Tools/Sp..._Tool_Kit.html

Having said all that, if you're just trying it out at this point and you don't want to sink $200 in the thing, then line your old nut up with the new nut (snicker, sorry, my inner 14 year old came out ) use a pencil to trace the location of the slots, and give it a shot with whatever you have. If you're pleased with the results, you can get the files and give it another try.

One other suggestion for us "do it yourself" kinda folks (though I've never tried it). I have a friend who actually buys his "bone" (snicker, sorry, more 14 year old stuff) at petsmart. He buys the big cow bones, which are pre-cured and cleaned for dogs, cuts them down, and makes his own nuts.