Upgrade from hubs to Switches

Within the last year we switched from Novell to MS Small Business server and upgraded our servers to two Compac Proliant 500 Mhz servers. We have about 40 users and find that our connections are still slow. Now we are being told to change our hubs from two DynaStar 24 hubs to a cisco 3548. We need expert advise or assurance that we are not being sold on another change with little results. Is this the correct way to go and what will be the results?