http://www.peavey.com/products/brows...ck%20Widow.cfm
Find the model of your amp, see if you can get the manual at peaveys site, or see if there is a model# on the speaker.
If its a black widow you can take the magnet off and put it on a new basket. Cheapest way to fix it.
Puting another brand of speaker in it will usually not sound as good........cabs are designed to work with specific speaker specs that is way more rocket science that you or I don't want to get into.
Some peavey speaker models are avail in 4 or 8 ohm. make sure you get the same ohm rated one as yours when ordering a new basket.