If you are recording guitar-driven rock, the plugins that come with ProTools LE surely can do the job. I find that there are other plugs that will sound better, but the DigiRack can serve the purpose. You will pay for higher quality plugs. For recording rock, you will need to get familiar with your compressor, limiter, equalizer, delay, and reverb for a start.
Specifically, I think that the Maxim limiter is workable and the D-Verb is passable when used tastefully. The Bomb Factory 76 compressor is definately useable. I find that I still use Digi's EQ3 quite a bit ... very nice sounding and easy to "dial in." You may not need to consider another EQ plug for a while.
When you are ready to upgrade your plugs to something with a more intuitive interface and improved sonics, I feel that you get a good value for you money with stuff from
Elemental Audio and
iZotope . Both companies have reasonably priced RTAS plugs that are very useful for rock applications. You may get a LOT of mileage out of iZotope's
Ozone .
All of this is IMHO, and naturally YMMV. When you are starting out and don't have much money to play with, I feel that PTLE gives you enough tools to do what's important: making music.