You can do it in VS 2008 too. I'm sure there's many ways to do it, but one way is to right click on the red dot in the margin of an existing breakpoint & select condition...
, then just give it a condition that evaluates to a bool
and it will only break if that's true. The conditional statement should have access to anything that's in scope at the line where the breakpoint is set.
There's also other options in that context menu that allow you to filter what will cause a break (for example only certain threads), break based on the number of times the breakpoint has been hit, run macros when you hit the breakpoint, etc.