If you mean printing using the print function in php I dont think you can do it in the *nix world quite yet. If you mean just printing in gerneral check out
http://www.linuxprinting.org/
This has some good drivers, and stuff. And gives details on how to set stuff up. If you mean to print from a webpage to a printer using say lp or something you could do something like
1) Create a temp Text file from the php page
2) call lp or whatever printer daemon is running
Hope this Helps!
