To activate Market app of Android in Iran,
you have to use a virtual private network configured by network settings (e.g. Xperia X10),
then run Market Enabler or remove your SIM card.
Market Enabler free version could be used
when your phone was rooted,
but the shareware version of Market Enabler could help too.
VPN was reset occasionally so you can only use it for a while!
It's the main problem of VPN PPTP connection in Android 2.1 and earlier versions!
To use vpnof your android you could share freevpnconnection from your pc!
It needs extra hardware.