Get WinGimp!

Seriously, though, Photoshop is more than adequate, but you'll need to offer some more information for accurate instructions...
Although I suspect that you just need a DDS plugin (and presumable permission to install it...) to open the nameplate file. If not, just create a new file, make the nameplate with appropriate colour and text with transparent edges, then save it as 32-bit (RGBA) TGA file and it should work at least to my information. Conversion to DDS befor edistribution is advisable, though... you can get NVidia's official DDS Utility tools (nvDXT) from
here; it doesn't have win on it's name though so that may be a problem, but since it's made by a company it can't be a virus so you'll likely have no problems getting it installed.