iMac superdrive is dead- what replacement do I get??

Here's my problem- my iMac's superdrive no longer works- won't read or write DVD's at all.

So was wondering if anyone here could help- should I get a new internal drive for my ageing iMac or should I get an external burner?

Taking apart the iMac to fit it isn't a problem as I've already replaced the internal hard drive in the past but I'm unsure as to what drive I can fit and still keep iDVD supported burning etc.

If I get an external firewire burner is it possible to boot off that to install Tiger?

Any help would be gratefully appreciated.

THANKS!!!