Near the top, there are the items "Home", "Help","Staff" etc.
Select the "Profile" option, and the "Forum Profile Information" item on the left hand side.
Scroll down. there is a text box for entering computer details.
The result? Every post will have a "specs" hover-over item, with the other data such as OS, Posts, Thanked count, etc.
For example; as you can see to the left, there is a "specs" item. Hovering over this will display the specification of my PC.