Thank you for your help, Joe1962.
a) I have no idea how to find an upgrade to vl-hot. GSLAPT reveals nothing. I rooted around a little in veclinux-current; don't know where to look for it.
b) The card reader says "GE high-speed 10-in-1 USB card reader". That's all I know about it.
c) I now know that /var/log/messages says " Vendor: notwork Model: CF Card CF Rev: 1.6E" no matter what card or combination of cards I actually plug in -- SD or anything else. As the mechanic said in the movie while observing that the car has no engine, "THERE'S your problem...." There is no reading of any actual card or cards, so naturally nothing can be mounted.
d) I have no problems mounting any card or combination of cards I put into this reader under my old setup, which uses kernel 2.4.
e) Output of 'fdisk -l' after card reader with a card (or two cards, or none) is plugged in:
Disk /dev/hda: 81.9 GB, 81964302336 bytes
255 heads, 63 sectors/track, 9964 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 1224 9831748+ c W95 FAT32 (LBA)
/dev/hda2 1225 1953 5855692+ 83 Linux
/dev/hda3 1954 2077 996030 82 Linux swap
/dev/hda4 2078 9964 63352327+ 5 Extended
/dev/hda5 2078 2442 2931831 83 Linux
/dev/hda6 2443 3172 5863693+ 83 Linux
/dev/hda7 3173 9964 54556708+ 83 Linux
Disk /dev/hdb: 300.0 GB, 300069052416 bytes
255 heads, 63 sectors/track, 36481 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/hdb1 * 1 36481 293033601 83 Linux