I've tried pressing each of the function keys during startup, but haven't been able to get safe mode as an option. Is there another way?
If F8 or other function keys don't work, you need to use MSConfig (Start > Run > msconfig). Select the boot.ini tab, and tick the /SAFEBOOT option. Then reboot.
Note that to restore the normal behaviour you'll have to use msconfig again to remove the tick while in Safe Mode.
More info here
The key should be F8. But there's a very limited window when it will actually get picked up. It's after the POST has finished, but before the "loading windows" has come up. I usually just start tapping the F8 key towards the end up the POST process. It should bring up a text based menu that includes Safe Mode as an option.
BootSafe - makes rebooting in Safe Mode a snap.
BootSafe takes the hassle out of rebooting in Safe Mode or back to Normal mode. No more fighting with the F8 key or MSCONFIG!
Bootsafe is freeware and portable (does not require installation).