MS ISA Server behind PIX 515 firewall

About a year ago we implemented a PIX 515 firewall and did away with Border Manager as our network firewall. Unfortunately we don’t have a way of monitoring internet usage unless we buy a product like WebSense, which supposedly integrates with the PIX.

Since we’re now a Microsoft shop I was thinking it might be possible to deploy ISA Server as the internet proxy behind the PIX firewall.

I haven’t been very successful finding any documentation on using these devices together.

Does anyone have experience with this or ideas on how to configure?