Thanks for your additional suggestions. I have everything working except one external HD sharing and believe it has to do with permissions. What I did:
Up until now, I had been disabling smart firewall and anti-virus on Norton Internet securing 2010, but decided to unplug the DSL cable to the router and removed Norton Internet Security 2010, Norton Utilities and Spysweeper from all four computers. I plugged BUSINESS PC (now named SPARE)and ANN (no name change) into the router. I re-named the SPARE back to the original name (BUSINESS) and rebooted; then removed all shares from that computer, rebooted; and then renamed SPARE, rebooted and then (with Simple File Sharing still unchecked), I confirmed ownership, as you had suggested and then set permissions and rebooted. SPARE external HD and My Docs now share with ANN properly and vice versa. I added RADIO (no changes) and confirmed sharing works with all 3 computers properly. I added the final computer MAIN (originally BACKUP2ME)and went thru the same renaming process back to BACKUP2ME and then back to MAIN after setting permissions, etc as above. Everything worked!
Then I reinstalled Norton Internet Security 2010 (NIS)and found that SpySweeper is not compatible with NIS so removed it from all PCs. I added Norton Utilities, rebooting after each change. I plugged the DSL cable back into the router and did the updates and scans. Now everything shares except the external HD on MAIN! I have not re-enable Simple File Sharing, yet on any PCs. The error msg I get is: "\\Main\External HD is not accessible. You might not have permission to access this resource. Contact the admin of this server to find out if you have access permissions. Not enough server storage is available to process this command." ANN, SPARE and RADIO all have the same message. Note that I am on a WORKGROUP and not a SERVER domain.
Originally I had a static IP address on BUSINESS (now MAIN) but used dynamic addressing on the other 3, I did this for port forwarding that I have on the modem and router for other applications. When I made the name changes, I put static addresses on each PC as I was told that they should all have static or all dynamic, but with port forwarding, to a specific PC, I should assign unique IPs to each PC. In addition to the 4 PCs, I have a ZOOM wireless adapter connected to my DirecTV Tivo. This device is on the workgroup addressed to the the MAIN PC. This continues to work fine.
The only remaining issue is the External HD on MAIN. It is visible from all the PCs but not accessible from any, except MAIN. I don't know why the External HD on SPARE works fine, but not the one on MAIN.
I notice that when I access MY Documents/Properties/Security/Advanced I have a box checked "Inherit from Parent the permissions entries that apply to child objects..." and an unchecked box: "Inherit permission entries on all child objects with entires shown here...". However, when I access either External HD/Properties/Security/Advanced I only have an unchecked box "Replace permission entries on all child objects with entries shown here that apply to child objects". I don't know if this is related to the problem since External HD on SPARE works and External HD on Main does not.
I haven't tried to setup the network again.