Prior to formating the hard drive of an older machine I wanted to store my data on another computer. I thought running the data through a network cable would be too slow for my taste so I removed the drive from my old computer and stuck it into in my newer one. I connected the drive with my IDE cable (which already had a DVD-burner attached) and booted up. Performance was terrible. I thought that maybe it was a master/slave problem. The drives have no writings on them telling me about the jumper settings and the manuals are long gone so I simply disconnected the DVD-burner. Performance was better but as soon as I started copying the files my mouse started to lagg. I have no idea what's happening but surely this indacates something isn't right. HD Tune 2.55 reports that my transfer rate is 1.4 MB/s. It also reports its temperature being 50C/120F degrees witch is a ~10-20C/15-30F degrees higher than my other drives. Im having a hard time imagining this being the cause though. I tried updating my drivers in the My Computer->Manage->Hardware but it couldnt find any newer drivers. I have a ASUS P5B SE motherboard. The only options available in the BIOS IDE Settings menu is: Sata Configuration: Disabled/Compatible/Enhanced Configure SATA as: IDE/AHCI IDE Detect Time Out: 0/5/10/15/20/25/30/35 JMB363 RAID Controller: Enabled/Disabled JMB363 Mode Select: RAID/IDE/AHCI I downloaded the manual for the MB but strangely it didnt explain more thuroughly what any of these do. Any help would be appreciated.

Check your IDE cable. The older cables were purely 40 wire conductor cables. However, when IDE updated the standard it increased the number to 80 wires (the extra wires are just more grounds to limit crosstalk).
However, using a 40 wire cable on faster drives will make them behave very slowly.
Though, the other possibility is the drive is dieing. Does hd tune turnup any bad blocks under its error scanner? Does the SMART report look ok?

Could be the device defaulted to PIO mode instead of DMA mode. You can check this under the device properties on device manager(assuming windows).
PIO mode meaning the CPU manages IO vs the DMA controller.