Looks like a normal VIA KT133, I've owned a few... beware that if you put a soundblaster live or newer in it with ACPI turned on, you'll get horrible crackling whenever the bus goes idle in windows. You have to turn it off and manually assign all your IRQ's with a lot of sound cards.
I am very certain it has a SCSI 5.25 drive.
Standard floppy -- 5.25" drives use the edge card connector, universally. Only on 3.5's did they go to pin connectors, which is why most cables from about '84 to '98 included both since the wiring is the same. Your picture is quite clearly a normal floppy connector for a 5.25".
there's two blue connectors in the mother board which I think are IDE.
Correct.
There's also a black connector.
Floppy connector. Notice it's shorter. IDE is 40 pin, floppy is 34.
If you are having trouble with it seeing drives, are you using the right cables? Are you trying to use 40 wire or 80 wire? They both use 40 pin connectors, but the 80 wire cable has cable select -- If 40 wire, are you setting the drive select jumpers correctly for 'master' or 'single' instead of the modern 'select'?
Ah. And it seems to have 4 PCI slots plus one PCI Express X16 plus one PC express X2... at least that's what I think the slots are...
Nope... not even close. 5 PCI, one ISA, 1 AGP (which is what you should be using for video), and one... gah, I forget what they're even called -- nobody used them since nobody actually made cards for it other than dialup adapters... that's right, it's an 'AMR' slot. Most listings say it only has 4 PCI because if you plug in a ISA card, it's backplane occupies the same slot as the PCI next to it (since they face opposite directions).
WOWZA!!! $35 for a single 256 MB. I hope the one I was trying to put in there was like this.
Try these guys, they're my go-to for old RAM...
http://myworld.ebay.com/1-800-4-memory
Specifically:
http://www.ebay.com/itm/256MB-SDRAM-MEMORY-RAM-PC133-NON-ECC-NON-REG-DIMM-/330518040550
I recently picked up 256 megs of 72 pin EDO off them for $20 -- and that ten bucks for 256 megs of PC133 is an entirely reasonable price. They'll even sell you a gig for what crucial asks for 256.
http://www.ebay.com/itm/1GB-2X512MB-SDRAM-MEMORY-RAM-PC133-ECC-6NS-REG-DIMM-/230650344427
I put an IDE cable into the machine having not understood that the floppy cable was entirely SCSI.
I suspect you really don't know what SCSI is...
The onboard video output plug was causing me confusion as it had a male-out VGA setup.
There is no on-board video plug -- where you trying to plug it into the 9 pin serial port, or the 15 pin joystick/midi port?