. . .
Plus my Time Machine only has 40G left all of a sudden. Odd.
That's because you have a new HD. Everything on it is treated as new, and was backed-up again.
Anyway, how do I delete all backups from 08-today and start backing up fresh today?
Just erase the disk/partition, per #2 in [Formatting, Partitioning, Verifying, and Repairing Disks|http://web.me.com/pondini/AppleTips/DU.html] (or use the link in *User Tips* at the top of the +Using Snow Leopard+ forum).
As thetrudz says, just erase the drive. Time Machine will start over automatically.
If you're not sure how to do that, and your backups are on an external HD, see #2 in Using Disk Utility. If they're on a Time Capsule, use the Disks panel of Airport Utility (see the green box in #Q5 of Using Time Machine with a Time Capsule).