I'm upgrading the hard drive that came in my EEE laptop (1000HE) with a faster, larger one. The old drive was a Seagate Momentus 5400.4 160gb (ST9160310AS) and the new one is a Western Digital Scorpio Black 320gb (WD3200BJKT), but the big change will be the one from 5400rpm to 7200rpm - it's a much faster drive. I did a little research, and the consensus is that the faster drive will affect battery life, but only slightly. Say 30 min less than the normal 6-7 hrs I get on a charge. That's acceptable.
The old drive was partitioned in halves, approx 75gb each for C and D. I'll likely partition the new one as one 300gb partition. I already moved everything that was on D over to C, and booted to make sure - then backed up C and made sure it was safely copied to the network.
I use Macrium Reflect Free to do my backups, and I'm going to restore the old backup to the new drive and just expand the target to the max during the restore. According to online support that Macrium gave to another user doing a similiar upgrade, it should be simple.
Here's hoping...