You have two relatively easy options sir.

Joikuspot which will turn your N900 in to a fairly comprehensive access point. This is a commercial application, costs less than $20 USD.

The free option is called "Mobile Hotspot" - you can download this through the application installer - I forget which repository it is in though. It's not as feature filled as joikuspot, but it will do what you need. The user interface on this app is nice, very simple and intuitive.