You can download the current version of SwitchResX here
Click here to
Download SwitchResX 4.3.4 (English/French/German)You can try SwitchResX for 10 days for free. If it does what you expect from it, if it solves your problem, you are expected to register the program.
You are not downloading a demo, but the full program. This is shareware, which basically means "try before you buy", not "try, solve problem, and trash".
SwitchResX - User manual
You can also download the Read Me file that is normally installed with the whole package above, as standalone download:
Click here to
Download SwitchResX Read Me PDF documentation (English)Older versions
For Tiger, SwitchResX 3.8.7 is still available here.
Older versions (for Panther, or even for MacOS 9) are available on this page.