As admin says, it's easy to do a search - here's what I do:
1) Power Sweeps search: put in the prize description. Especially if it is a one of a kind prize! Instead of searching for "guitar", which gave me 61 hits, search for "Daisy Rock guitar" - which gave me 1 hit - or whatever type it is. The less you search for, the better, so don't C&P the prize from the entry form or rules - break it down. I've had great success searching that way 8)
2) Latest or New Sweepstakes forum: check before you post if you don't find it listed: Same principle - take a main word from the title - the less common, the better. You can also use the EDIT feature in IE:
EDIT>FIND(On this Page)>in pop up box type your search word and keep clicking find next until it tells you it's finished or you find a post that matches.
Once you get "grooved in", this will save you lots of time, and reduce duplicate posts. 8)