Ok, I am starting a server-software project for an MMORPG, to create private servers. The client has encrypted packets. Could I be linked to a guide on decrypting packets, or a guide on packets in general too?

Well this isn't really related to MMORPGs but it's a great resource on reverse engineering game packets.

http://www.valhallalegends.com/

Check out the Bot Development forums, and the BNet Docs. It's a listing of all the Battle.net packets. Search the forums for packet decompression and decrypting, you'll find tons of info.

Thanks, unfortunately this isn't a battle.net game :P

And its being released soon (but its predesscesors packets were encrypted) so thats why I know it will, but i wanna know for when it comes out

No but the mentioned forums contain info on game related packets which will be very helpful.