We have used SilverFox and DigiBoard for this purpose in the past (with Fox2.6). I'm not sure if SilverFox is still available but Digiboard still is.

We switched to a different scheme whan moving to VFP and MSCOMM: we no longer use mutiple serial ports for two main reasons:

1) Low powered pcs are now relatively cheap.
2) Using a single pc for each data source improves the overall reliability of the system since one pc failure does not affect mutiple sources.

I would be interested in hearing of anyones experince using USB and say MSCOMM - does it work?

BTW we have developed a "standard" data logger system that provides for local intermediate storage of the serial port data independent of the transfer of data to the LAN server final location. This means that if the LAN is down for whatever reason, the datalogger continues to record the data which can be subsequently uploaded to the LAN once it is available again.