I know dumb question, but I have a iMac 6.1 with the new flat aluminum keyboard and pushing F8 key appears to only control or forward for itunes. Using the "fn" key in combo with F* gets me the "Space" screen.
Actually F5 should not be this key you want, pressing F8 is a standard(not customized) Windows procedure which shows up windows boot menu
You can also use Send keys to send,
ALso you can disable spaces for some time
