The only way to use wireless "g" with a DirecTiVo is to use an approved USB-ethernet adapter with a wireless ethernet bridge (or "gaming adapter"). Older versions of the Linksys WRT54G/GL/GS can be converted into an ethernet bridge. A ZyXel P-330W can be purchased for under $50, and supports wireless ethernet bridge mode.
For wireless ("b" or "g") and the HR10-250, you'll need a wireless ethernet bridge.
Some "b" adapters will work with a non-HD DirecTiVo (with further hacking). You'll either need to use rbautch's wireless script or drop netconfig.itcl into your /ptvupgrade/tivowebplus/modules directory and do a "Full Reload" of TiVoWebPlus to set wireless parameters.
A list of working "b" adapters can be found here. 802.11b adapters with three "green check marks" or "green thumbs" will work fine. The Hawking WU250 will work with a DirecTiVo running 6.2 (I have personally confirmed this). Disregard any "g" adapters mentioned, as well as any adapter that requires software version 7 (or greater). The TiVo-branded "g" adapter will not work with a DirecTiVo.