Dell Wireless 1397 WLAN Mini-Card too slow with new ISP

My native hardware/software on laptop "a" worked fine with Comcast (over 100Mb/s) np, but won't deliver more than 20Mb/s now with my new ATT Uverse plan. I'm getting 132Mb/s through the modem to another laptop "b", no problem. Dell won't help me because laptop "a" is too old. Can anyone here recommend a possible solution? Such as a different (possibly compatible) network adapter download link? Thanks for reading this. Cheers.