Using startup commands when the default startup disc is not OSX I have to use a startup command (ie command - S for single user mode) when restarting my computer, but this is proving to be impossible, as the startup disc is windows by default on my computer - unless I hold option at start, I cannot choose to go into OSX, and when I hold the startup command I want without holding option, my computer just goes into windows - it doesn't work when I hold a startup command after I choose to run OSX, either. 

Additionally, I cannot get into my system preferences to change the startup disc, as I cannot login (which is part of the reason why I need to use a startup command in the first place). I cannot change the startup disc on windows, either.

Does anyone have a fix for this?

OS is Lion, w/ a 2006 Mac Pro
You can boot to the Lion recovery partition by holding the option key during the reboot.  From there, you can select the startup disk, similarly to if you were running system preferences.

From there, the single-user mode boot should work as you expect.