Does it have a PCMCIA slot? If so, one of [link|http://www.bb-elec.com/product_family.asp?FamilyId=23|these] might do the trick for you. They're not cheap though.
You can even get an [link|http://www.bb-elec.com/product.asp?sku=DC-WSP-01-S&TrailType=Sub&Trail=26|802.11 to RS-232 serial converter]. It's even more, of course.
There are probably cheaper solutions out there. This is just to indicate there are many ways to skin this particular opossum.