Migrating to Gigabit Backbone

[techspl]

Hi All,

I have a fast ethernet network and I would like to upgrade the backdone to Gigabit.

Each site has stacked 3Com 3300 switches with either a 3Com 3300-FX switch or a 3com 3300 switch with dual 100BASE-FX module connected to the stack as well as a layer 3 module in each of the stacks.

All sites are connected using multi mode fiber.

How do I get gigabit on my backbone?

I'm thinking that I can buy:
(1) Two (2) 3Com 4200G swicthes each with a 100BASE-FX SFP module and a 1000BASE-SX SFP module.
(2) Two (2) Gigabit Multimode Extenders (allied Telesyn)

I can then connect the 4200G 1000BASE-FX SFP to the 3300-FX switch. Then connect teh 4200G 1000BASE-SX to the Gigabit Extender and repeat at the other end.

This should work, right?

I'm not too sure if the 3Com 4200G supports the 100BASE-FX SFP modules though. Maybe the Cisco 2960G?

Any ideas will be much appreciated.

We do not have the budget to replace all switches so I have to plan carefully how I would upgrade the various links to Gigabit speeds.

Thanks,
techspl