Network gurus: Certain website won't load on OSX but works on PC

So my company's web admin has always worked just fine on Mac until Friday when trying to use a particular page (while saving/posting data). It sometimes takes 20 seconds to actually successfully post data and get to the next page... other times it will hang there indefinitely. Tried it in Firefox and Safari. The weird thing is, it appears to be only happening on the Macs in the office. I hooked up a PC Laptop to my ethernet cable that was in my Mac, and the PC loaded the pages just fine (Firefox & Chrome). But I also tried using my virtual Windows install (VMWare + IE) with no luck either. Not sure why this started happening on Friday. What are the possible scenarios? I should also note that this website is only accessible on the local network.

Thanks for any help!

I suggest taking the issue to the department in charge of maintaining and coding the website since it is internal.

They say they're not going to support Mac issues and to get everyone PCs instead.