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I agree with MichaelWilliams. As his answer pointed out, it is a marginal level of security, but far better than nothing. Enable MAC address filtering and disable SSID broadcasting, and I do think it would be borderline ok to continue to use for a home network. Not ideal though.
You would be better off getting another router. WEP is easly broken by any kid with a laptop and copy/paste scripts. If anything, using WEP is better than nothing, not by much though. You will at least deter a basic Windows user from logging on, one that would log onto an unknown network that could compromise their own system. Look if your router can do MAC filtering and disable your SSID broadcast, again, it's better than no encryption at all.
Depening on your computer skills, you might want to consider looking for a used router. Using Craigslist, I've purchased a Linksys WRT54g router for about $10, slapped on DD-WRT and then tweak some settings; made for a very decent router.