Hub 2 Hubs

Hi everybody
I have one 16 port hub upstairs with 4 PCs , and downstais I have 16 Switch with 8 7 workstations and one domain server (WINdows NT). Again I have another hub in another ofiice with 4 PCs. My problem is : there is no conection between the two hubs downstairs (Can I connect one hub to two hubs?). Also the LAN is very slow..Help…. Help..Help.