1. If you just want to type numbers, and not use them in any
calculatiions or computing or entering dates etc., you will find them
at Unicode 06F0-06F9. (Go to Insert Symbol, Arabic.)
2. If you want your computer to use Persian-style numbers rather than
Western numbers, then go to Start > Control Panel > Regional and
Language Options, and the first panel that appears lets you change the
display of numbers. (It's different in XP and Vista.)