Project -> Add Track -> Ad FX Channel (or at least that's how it runs in SE3; it should be similar enough irrespective of the version of Cubase being used). You then specify the effect and blend the processed signal with the dry signal via the 'send' button on a given channel strip.
Or at least that's the theory and how it would work with things like delays and reverbs with wet/dry ratio set to 100/0. Generally, EQ, compression, gates, and gain staging are better to suited to being used as inserts as track transients differ quite a bit. the exception is drums which generally take a compression bus quite well. If RAM and CPU power are an issue, you can always bounce the individual tracks down with the effect applied - it'd be good idea to turn off the effect and disable the original track, which means it's always there should you wish to tweak the compression settings.
I like the T-Racks stuff, warms things up nicely when used sparingly.