Simple guide in Photoshop:
Before Anything Else: Make sure you download VTFEdit. Lets you view the contents of GCF files, save as vtf and vmt etc etc. Also, having photoshop could be pretty vital too.
1. Make a new image sized 64x64.
2. Make sure you have a layer that is filled with white.
3. Create a new layer and make your crosshair on it.
4. Center it by selecting both layers, then Layer > Align > Vertical Centers and Layer > Align > Horizontal Centers.
5. Select the crosshair you made by ctrl+clicking the small thumbnail next to the layer in the Layers Pallete.
6. Go into the Channels Pallete and click the 2nd button from the left at the bottom. This will create a new channel, with a black and white outline of your crosshair.
7. Now save it. Name it to anything you want, but make sure you select targa from the Filetype drop down. Just leave it at 32 bits.
8. Open VTFEdit and then File > Import > YourCrosshair.tga. Just press OK when the settings box comes up.
9. To see if it worked, go View > Mask. If it has a transparent background after this, it'll work ingame. If not, you're doin' it wrong.
10. Save it as a vtf file. (File > Save As > Name it crosshair8 if you don't have any custom ones).
11. Now in VTFEdit, navigate to your TF2 Materials GCF file. More specifically, tf > Materials > VGUI > Crosshairs and extract a vmt to your desktop.
12. Open this vmt in VTFEdit, and change out all the bits with numbers to 8 (crosshair4 becomes crosshair8 etc.)
13. Save this as crosshair8.vmt.
14. Last step; Grab both crosshair8.vtf and crosshair8.vmt, and chuck them in your tf\materials\VGUI\Crosshairs folder. If those folders aren't there already, create them.
15. Boot up the game and you should be able to select them from the menu.
Enjoy making dick-shaped crosshairs.
