The biggest thing you need to watch is if the 5 volt Key (notch) is in the card.
Advertisers aren't always that great about giving the voltages.
If the 5 volt Key is there then it works in 5 volt slots.
An eSATA PCI-X (or even PCI) card is possible, yes.
http://www.newegg.com/Product/Product.aspx?Item=N82E16816124014http://www.newegg.com/Product/Product.aspx?Item=N82E16816318004http://www.newegg.com/Product/Product.aspx?Item=N82E16816111067