I shouldnt really matter. As long as the header you plug them into on the mobo is USB 2.0 speed, all the front ports are is simple wires and connectors, and has no real effect on the speed or version of USB that goes through them.
Like he said. It's all in the MB. Most systems have a couple of 1.1 and a couple of 2.0. The 1.1 are a left over from older chipsets and they then add the 2.0 with an extra chip.
And the wiring does matter. If you run a 2.0 device to a 2.0 MB over 1.1 cable you will likely get data corruption and drop outs. They use special methods to handle the higher speeds in the 2.0 cables. Same deal with Ethernet. Cat 3 wire is ok for 10 mbps but you need cat 5 wire for 100 mbps. You may get lucky on short runs but it's just that, luck.
Having said that. You might get by with the short run from the header to the front case connectors. If you have a problem there are drive bay connector panels. You might be able to buy one and canabalize it for the cable and connectors to swap out with what came with the case.
Locally Frys, Best Buy, CompUSA, amybe Radio Shlock
If all else fails contact Antec. Also, what MB? If it has all USB 2 headers all the supplied cables should be USB 2.