i bought my 8100 off ebay and when i inserted my sim card, it required a password to unlock it. is there anything i can do other than contact the seller? because they haven't immediately replied and i really need my phone! thanks!

You could leave appropriate feedback for the seller for selling you a locked device.

Just enter the password wrong 10x, and it will wipe the device of all personal settings from the old user. Likely it has an IT Policy on it from the previous user.
Remove IT Policy - BlackBerryFAQ

Good luck.

Is the BB asking for the device password or is it asking you to provide the PIN for the SIM?