Many HDs use a different jumper layout for Master with Slave than for single master. Many drives ship with an 80-line Cable Select high speed cable, and you have to set your drive jumpers appropriately.
Once you figure out the jumper mania, set up the 30GB drive as your slave drive, boot the 3GB, and set up the 30 as either 2 (16GB and 12GB) partitions or 1 28GB primary partition, and copy the entire content of the 3GB drive over. Then swap the drives once you are sure the 30GB will boot. Don't forget to make the first (primary) partition on the 30GB drive 'active'. Once you're satisfied with the drive layout, you can wipe the 3GB drive and use it for a download bin...
If the 3GB drive is not a UDMA capable drive (BIOS shows it as PIO only, not DMA 2 or better), move it to the secondary cable as master with the CDROM as slave. The 30GB will run significantly faster at UDMA speeds...