Thanks for the two responses. Based on the suggestions, I went back to my computers an started searching and changing. The good news is that both my windows 7 and XP computers now can see each other and share files. The bad news is that I don't know what changes I made to make this happen.
Something new regarding this problem - while watching a movie on my windows 7 laptop via WIFI to my XP computer, I lost the WIFI connection. After testing I found that when our wireless phone received a call, the WIFI connection got zapped. I guess the phone is on the same band width as my WIFI (2.4).