Thanks, Tomorrow. But is there any way of moving the info already on my old hard drive?
Well, if I may play Devil's Advocate, why would you want to?
Think of it this way - you bought a bigger drive for more Time Machine capacity. You could theoretically do this in one of two ways:
1. Move everything from the old (smaller) drive to the new drive, taking up quite a bit of its capacity, then perform incremental backups from that point. Keep the old drive for...whatever sounds good to you.
2. Leave everything on the old (smaller) drive, giving you even more space on your new, larger drive. Keep the old drive, just in case you want to roll back even farther than the data on your new drive.
Either way, you'll have a complete backup on your new drive, you'll have all your old data, but with option 2 you'll have even more blank drive space available.
But to answer your question more directly - I imagine you could use some sort of disk clone utility to copy everything over to the new drive, I can't vouch for one because I've never used one. But I suppose it's possible.