I am wondering if an user can log onto my domain outside the office, or are you only able to do this locally? (in the office)
Can you be outside the town or even country login onto a company's domain? (windows server 2008)
Sure, as long as you can access the company network, which is normally what VPN's are for.
Once VPN is defined in the workstation, the login screen even offers the option to FIRST loginto the VPN, THEN process the user login.
Standard functionality in a LOT of companies.
"or even out of country" is idiotic, btw. - this is internet, and the internet doesn ot care whether you are across the street or in another country, as long as the internet connection is available. THe only sensible discintion is "inside company network" and "outside company network, requiring something like a VPN".
Your users will be able to logon to their computers using "cached credentials" (default is to store the last ten logons), then you can connect using any VPN to your work network, and access the "domain" as it were. The only real restriction is roaming profiles, which get borked if you logon without being connected.
If you are talking about logging on using an domain account that hasn't previously logged onto a computer remotely, then see TomTom's answer (and comments), unless the users have "local accounts" on the machines, and then use domain accounts to access the network, that also works.