How to print over the internet in windows XP?

Depends on the DSL router

The answer is maybe.

The router may be configured by the manufacturer to only accept print jobs from the inside. You may or may not be able to reconfigure that.

If you cannot, Try forwarding a TCP port from the outside to the TCP port for the inside print server. Here are the basics of that idea...

Do you already have it set up to print from the PCs in office B (from the inside of the DSL router)? If so, you may be able to set up a port forwarding rule.

Lets say, for example, that the DSL router's internal ip addy is 192.168.1.1 and that to print from the inside (office b) you set up a printer on each computer to print to 192.168.1.1 port 9100.

So set up a port forwarding rule on the DSL router so that incoming traffic to port (pick an unused port) gets redirected to 192.168.1.1 port 9100 (TCP)

Then set up the computer in office A to print to the static ip addy of dsl router (specify the port you chose on your port fwd rule).

I would not choose 9100 on the outside side because then anyone can print to your printer. pick something high that isnt used.

9100 is a guess at what port it uses, another likely candidate is 515.