You need to read the manuals. Most are available on the CDs that come with the switches. failing that they are available on line on the 3Com website, you do not need anything other than a good web connection to get them.
You need to read first and foremost the implementation guide, this will cover all the processes needed to create VLANs use 802.1Q to tag traffic between switches and also explain the use of spanning tree rapid spanning tree link aggregation and flow control. They are not an arduous read they are pretty easy on the brain and most of what you want will be covered step by step.
You will need the quick reference guide to show you all the commands and help you familiarise with the interface.
Ensure you have planned the whole network before starting, make sure you know which ports do what and which vlans endstation ports will be in.
Make sure you have the latest code for the switches, especially in the case of the 4900 as you will need layer 3 support. The code is also available from the 3Com website.
I could take you through step by step,but given that I have no idea which model of 4900 you have,or which software revision you have on the 3300s, this could be more time consuming than you reading the manuals. Besides you may not actually learn anything, if you read you will.
I would also set up 3NS or Network Supervisor, to help you manage all the switches and tweak the network.
I hope this helps.
