$250 - $300 range. Maybe a little more or less depending on how bad the buyer needs a new tower. Keep in mind that this is based partially on the price of APU systems at Wal-Mart that will offer similar performance.
I see the E 6500 listed for $40 now on ebay and it hasn't sold (for a basis of parts)
I see a bunch of the 1 GB 9800gt video cards listed for $20
I don't see your exact motherboard on ebay but the close one or similar ones are going for anywhere between $40 and $75
$15 to $25 on the 250 GB hdd
The hyperx might bring you $50
And as for the case, unless you have a local pickup it's probably not worth shipping. Usually something about that size will cost between $12 and $20 to ship at the economy shipping unless you have a business shipping account.
At an educated guess??? I would say you might possibly get $175. Minus the shipping costs and ebay fees if you are an ebay guy like me. Otherwise, if you have something like cregslist or something like that were you are you might have a chance at unloading them that way. Clean them up real nice and put them all together in a working unit with windows XP and a local pickup sale might bring you a little more. Still $175 from parts will get you started on a new one.
I have a similar setup for my home server, it has the E4500 DFI DK P35-T2RS motherboard, but I also have 4 gigs of memory and 3 - 1 TB hdd and 1 - 2 TB hdd and I use it for a home server and well as streaming wireless video to my wireless samsung bluray player. Hence, all the hdd space lol. It stores movies and pics that I can watch on the big screen in the living room including the 3-D movies. So you can, for a little extra make use if it. I'm just saying.