If the external drive is USB then it won't matter if the drive inside
is PATA or SATA however it will run slower than if used on an internal
drive. Best would be to fit an eSATA card and use an external caddy
that has eSATA connection - that way you get the full interface speed.

Regarding USB - if you have a USB3 port then using a USB3 caddy will
also give you full speed but at a higher cost than eSATA until prices
of USB3 devices start to drop.

Just a warning if using an external caddy - be sure not to disconnect
accidentally when booted into Windows. At the least it will corrupt
data and at the worst totally trash the OS