Thanks, that opens up some money-saving possibilities! :D
I have some 4108 modules if you are interested. What are you after?
It's not available from the web gui only a console session either direct to the switch or telnet
Dont replace any of those switches its a good stable setup, i ran that setup for years and i can pretty much guarantee you won't even be getting close to maxing out the 4108.
You can get a 6x gig port module or a 20x gig port + 2x mini gbic module for the 4108, which you can get off ebay fairly cheaply.
As others have said it does support LACP but from the command line. I wouldn't recommend using the web interface, its a horrible java interface which is very limited and can be very buggy depending on the firmware level.
The cli (and don't mean the menu) is very powerful and will give you access to all the features on the switch.
If you want a cheap core you could always get a procurve 2610 which has layer 3 features........not ideal i know but i use one as a layer 3 switch and does the job perfect!
If money's tight I would recommend monitoring the network usage before upgrading anything. Have a play with PRTG or The Dude, these can be used to gather port utilisation stats from the switches. Find out if any of your links are heavily utilised and take it from there.
Cacti is also very helpful if you have a linux box kicking about to run it on.