Static IP routing

Hello, well first of all I have had a little look around to see if anyone asked what I'm about to ask and I have found one remotely simillar query but it does not exactly (I think) outlines what I'm interested in.

I have recently signed up for an ADSL line with 8 static IP's and not much later after that I wondered if there was a way (software/hardware) to enable outside users (internet) to mask their own IP address using one of the IPs from my IP block with simple username/password authentication without my PC having to use that same IP address for them to be able to do so.

For example each username would have different IP address assigned to it and when that user loggs on s/he could view a web site without revealing their own IP address.

I'm sure I'm not making much sence but any input (even if only scratching the surface) will be welcome indeed.