internet slow!!!!!!!

ok so here is what's going on I have a home network at my house set up with a linksys wireless G router......and there are 3 macs connected to it wirless one mac is wired and one windows machine....now the net work has been slow for a while but only for web browsing(already tried diferent browsers even Omni web) but browsing is as slow as it can be but for some reason downloading is very fast getting up to about 700 Kb/s now this does not happen on the windows machine it seem faster then the others much faster on web browsing....and the download is about the same.....
is the router being bad with my macs.....
or is my cable company screwing me ohh yeah some websites are not going in like overstock.com never loads on any machine help I know its a lot but any suggestions??????