I have recently setup a homegroup between 3 PCs (Windows 7 x64 all 3 computers) in my house via hardline and my router. My router is a Linksys WRT54GL 802.11b/g with Tomato Firmware installed. My internet was fine prior mind you and nothing has changed. It seems like my over-all browsing has been delayed a little and my downloads "slowed" since I networked the computers.
Nothing horrible but my normal downloading off a site I like was 1.6mb but now I only get 400-800kb. I am also unable to max my connection, so if I load 4 downloads from 4 different sites I stick around 400-800kb.
Is this normal or is there perhaps some settings either in my router or the homegroup that COULD effect my speeds? Also does homegroup use a set of ports that I perhaps need to forward?
Windows 7 Slowdown 
