That networking equipment is pretty low-end - although the switches have a lot of ports, they simply aren't capable of handling much load, and there's nothing that can really be done about  than either not using Ghost's default multicast mode of operation and specifying Unicast transmission (which will be quite slow with only 100mps, but won't impact the other switch ports), or dialling back Ghost's transmit rate to the point where the switches can cope. If they were unmanaged gigabit switches they'd probably cope better but using 100mbps gear for this is pushing it.

A network with unmanaged switches means the switches won't be aware of IP multicast and will just try and stuff all the Ghost traffic down every port, and very low-end switches may not handle high offered loads well in this case. Standard TCP/IP multicast in switched Ethernet works best when you use switches that support it (using a feature called IGMP snooping, in concert with a router that itself supports IGMP and can produce IGMP query packets), in which case only the switch ports participating in the Ghost session receive the traffic, while the Ghost server still only sends each frame once and so the link from the server to the switch doesn't get saturated as it does with Unicast.

To get an idea of the switches that work best with Ghost at that kind of port count, have a look at this HP Procurve selection guide (which helpfully lists the series numbers for other vendors in the same categories, so you can compare them up; look for switches with IGMP support, which means a managed switch like the Procurve 2510G, Linksys SRW 2024, 3Com 4200G or Cisco Catalyst Express is the level of gear to aim for (in conjunction with a suitable router to generate the IGMP queries for the switches to snoop).