Yes inputting the service tag unfortunately does not yield a full set of system drivers in many cases like it used to. I have put through this complaint on IdeaStorm.

Although you shouldn't put in your service tag as it can be used to identify you (I will edit it out your post). I have used in this case to look at your original configuration to see what you have missing. Your Vostro 1400 should have the following drivers:

1. Notebook System Software R181862.exe
2. Chipset - R161772.exe 
3. Video R165797.exe
4. Intel Storage (serial ATA) - R154200.exe 
5. Conexant Modem D330* R167368.exe, R148605.exe, R147130.exe
6. Sigmatel Audio - R171789.exe
7. Knowles Acoustic Driver R166782.exe
8. Broadcom Ethernet R155246.exe, R151336.exe
9. DW1390 Wireless Card R205204.exe
10. Dell Quickset R286806.exe 
11. Touchpad/Pointing Stick R165804.exe 
12. Webcam Driver R165116.exe
13. Dell Webcam Centre R230103.exe
14. Dell Support Centre (Optional)

*There is no mention of the modem in system configuration but the modem is usually standard. I would try installing it, R167368 will fail to install if you have no modem, if thats the case you should ignore R148605, R147130. In Windows XP failure to install the Conexant drivers before the Sigmatel drivers sometimes causes audio problems.

If you need any more advice on Windows XP reinstallation follow my wiki A Clean Install of Windows and use the drivers I have mentioned above. Ensure there are no errors in Device Manger. 

Although its important you have all your drivers installed, reinstallation of Windows XP will likely not solve your keyboard problem. From the symptoms you are mentioning it is likely a loose connection of the keyboard to the mainboard. 99 times out of 100 reseating the keyboard fixes the problems you mention. Follow the instructions in the Service Manual for keyboard removal, then reseat the keyboard. It should be quite straightforward. If you have any additional problems or that doesn't work post back.

Thanks for your post and links.

At this point, given that drivers were/will be installed out of order, should I do another clean install of win xp?  Or should I just install all of the drivers that you list in order and not worry about the drivers that were already installed?

Regarding the keyboard problems, I haven't had a key stop working for several days, but I my cursor occasionally jumps elsewhere while I'm typing (as if I clicked to some other part of my text with my mouse).  Neither of these problems took place before I did a clean install.  Given this, do you still suspect a physical connection issue rather than install-related?

Thanks,

Stan

I just had my cursor jump while typing email, and it actually jumped to where my mouse was.  So it seems that I'm getting a false mouse button event.

Sorry we missed 2 drivers:

11. Touchpad/Pointing Stick R165804.exe 
12. Webcam Driver R165116.exe
13. Dell Webcam Centre R230103.exe

*I think the webcam is optional 12 and 13 may or may not apply.

Try installing them and the others you are missing. If you still are experiencing issues attempt the reinstall from scratch with everything in the correct order. Again if that doesn't work, try reseating the keyboard and also the touchpad connectors to the mainboard.