How can I make new partitions available? (maybe repost)

["Christian Pernegger" <pernegger@chello.at>]

[I could've sworn I posted this question yesterday, but I didn't get a
copy nor can I find it among my sent messages. So forgive me if this is
douple post.]

When I've created a new partition using cfdisk, how can I make the kernel
"see" it without rebooting?

When I try to create a fs, mke2fs bails out with

"Device not configured while trying to determine filesystem size"

I know from earlier experiments on other machines that a reboot would
fix this, but I'd rather not take the box down.

Thanks

Christian