Since the introduction of the orange box, the orange box's updated material system now allows for tags/keywords to be placed on textures.
All TF2 textures have a common keyword, so.. what this means for this question:
1. Open up hammer and a map as normal.
2. Go to the texture browser.
3. In the texture browser, find the "Keywords" field. (linked below)
4. Click into it and type "tf", without quotes of course.
5. Only TF2 textures will be loaded. It will take a few minutes (a long few minutes) seeing as its your first time doing it. Dont try to exit it or end task it, it will appear frozen but its not :/
6. Enjoy undisturbed TF2 textures ;o
Unfortunately there are no tags on any textures from episode 1 and below, so you wont be able to punch those up.
Edit: Crap for 10 minute late response ;o
I uh.. Left the window up in another tab for a bit before actually deciding to read it, let alone refresh it to see if someone else answered it.