Do you already have a DI-624, or are you just attached to Super G?
One of the easier solutions is probably as Jack suggested -- get a Buffalo WHR-G54S or something similar (another Buffalo, or e.g. a Linksys WRT54GL). A Buffalo might do most of the job out of the box. It can do the job via one of many third-party firmware such as DD-WRT. It could connect in "Client Bridge" mode with a DI-624 or any other standard 802.11g router or AP, but not in "Super G" mode.
There are other off-the-shelf "wireless bridge" devices under various labels which could do the same job, typically with less flexibility and usually higher pricing and reduced availability. But if you find one that does the job, it should be simpler to set up, as it's meant to be used in this way. (I've used a Netgear WGPS606 for this purpose, and it's very simple to set up for wireless client bridging -- it's best regarded as a simple wireless client bridge with a so-so print server thrown in.)
A D-Link DWL-2100AP might be a Super G solution. A pair of these should certainly be able to do the job. One of them can at least do part of the job, connecting as in Client Mode with a DI-624, probably in Super G. Possibly not in Client Bridge Mode though, which would mean that there could be difficulty in having computers on both sides see each other.