From DD-WRT Wiki
The WRE54G is an 802.11g wireless repeater sold by Linksys. It uses the WDS protocol and is compatible with a number of Linksys routers and access points using the stock Linksys firmware.
 Hardware Revisions
There are three hardware revisions.
- Revision 1 - Broadcom Chipset, 2MB Flash, no ethernet ports
- Revision 2 - Marvell Chipset, 1MB Flash, may have ethernet ports
- Revision 3 - Marvell Chipset, 1MB Flash, may have ethernet ports
Only the revision 1 hardware is compatible with DD-WRT at this time. Marvell has not released drivers for their wireless chipsets, and 1MB of ROM is probably too small to be useful anyway.
The revision 1 hardware is very similar to a WRT54GS without the Ethernet switch, and can run most generic Broadcom builds under 2MB (after the initial flashing).
 Flashing to DD-WRT
A detailed tutorial is available for flashing the Linksys WRE54G v1 hardware to DD-WRT
The process can be summarized as:
- Upgrade the WRE54G to the latest Linksys firmware
- Flash a specially modified DD-WRT firmware
- Flash a standard build of DD-WRT through the web interface
 Additional Information
After flashing to DD-WRT, the WRE54G can be used as a WDS repeater, or in bridge mode. Potentially the WRE54G can be used for any purpose that does not require an Ethernet port. Although it has only 2MB of ROM, it has 16MB of RAM, which could make it useful for running services.
The main thread dealing with the WRE54G is located [here].