After taking a look at the types of DDR SDRAM available, I woder if my descision to go with 2 x 256MB PC2100 ECC Registered CL2.5 184 pin DIMMs to go with my Gigabyte GA-7DXR mobo...is there any real difference with the cheaper variety of the PC2100 type memory?

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AMD Athlon 1.4GHz
Gigabyte GA-7DXR
512MB PC2100 DDRAM
Hercules Prophet III
Dabs 15.1" TFT DVI
Hercules Gamer XP
VideoLogic DigiTheatre DTS
2 IBM Deskstar 60GXP 20GB
Mirai 40-16-10 SCSI CDRW
Pioneer 10X 40X SCSI DVD
Cooler Master Aluminuium 201 case w/400w PSU