If your Backups are ESR-Games, you could install it directly through HDL, but if it are 1:1-Copies, do it as said before with WinHIIP.
You didn't waste your money, if it is USB 2.0.
It is/might (possibly, or probably) slower than on internal-IDE, but it is an easier handling.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux