ahhhh, you're first post said you have a 865PE, but you just now said i856PE, i'm assuming you just had a case of dyslexia, but i personally have never dealt w/ TigerDirect....just heard of all the bad news about them, if i were you i would just go w/ the actual MSI site, and their qualifications for the correct RAM. Not sure if Tigerdirect just wants to sell to everyone to make a buck...you're call.
"Will mushkins RAM fit in my comp?"---well any 184pin stick will "fit" but being compatible is another issue.
but i know a lot of ppl who swear by Mushkin RAM, they seem pretty good...if you're really nervous, you could try emailing MSI and asking them...maybe their list hasn't been updated yet.
i see that tigerdirect has a limited amount of DDR400 RAM, ever think of shopping at www.newegg.com?
you'll be blown away by their selection.
Crucial, Corsair, OCZ, Kingston would be my first choices..seeing as MSI has already approved them.
but if you like to take chances, go w/ Mushkin.