None at all. I got both boards are samples directly from IWill and Gigabyte- one of the perks of my job is i get to test out all the new stuff and recommend which is best to the higher ups. Anyhow they both run fine.
The GA-7dx has 256 megs of micron memory, CL2.5, GeForce 2 MX (from eVGA) 800mhz Athlon (100mhz bus) and ATA-100.
The IWill KA266 has same amount/type of memory, same graphics card, 800mhz Athlon oc'd to 1Ghz on 100mhz bus and ATA-100. IWill does have a KA266R (RAID) board available, but they weren't willing to give it up to me or they didn't have them. So, I got the ATA-100 which is fine with me =)