can t network xp computers

Most of the time, my Vista computer can see my XP computer, but can't copy to it. For example, if I try to copy in Windows Explorer to My Documents on my XP computer, which is shared, it tells me that I don't have sufficient permissions. And I should ask my network administrator, which of course, is me. It's very frustrating.
My XP computer usually can't see my Vista machine and can never see the Public folder, where I've tried copying files in an unsuccessful attempt to use my XP computer to copy files from that folder to my XP computer.
It did work once, but never since then and I don't know why. I've used the Network wizard to set my Vista machine to the same workgroup as the XP machine.
Before I upgraded to Vista, I had it working consistently with XP by using NetBeui. I've never succeeded in networking any computers without it, but it doesn't seem to be available in Vista.
Any tips on getting XP and Vista machines to acknowledge each other?
Thanks, Ellen Dell M70 Pentium M 1.3 GHz 2 GB SDRAM NVIDIA Quadro FX Go1400 256 MB

Most of the time, my Vista computer can see my XP computer, but can't copy to it. For example, if I try to copy in Windows Explorer to My Documents on my XP computer, which is shared, it tells me that I don't have sufficient permissions. And I should ask my network administrator, which of course, is me. It's very frustrating.

Hello :)
This sounds like a permissions problem.
1) When you XP computer asks for a password, are you logging in with an account that has administrator priviledges?
2) When you shared the folders in XP, did you set it up so that everyone had full control? The default is read-only... which overrides your admin permisions over the network.

My XP computer usually can't see my Vista machine

This is usually caused by Vista setting the network as a public network, which strengthens the firewall so that other computers can't see it.
- Go to Control Panel -> Network and Internet -> Network Center - If next to Network category it says Public Internet, click Change to private - If next to Discovery and Sharing it says Blocked, click Allow

and can never see the Public folder, where I've tried copying files in an unsuccessful attempt to use my XP computer to copy files from that folder to my XP computer.

Yes, there are some terrible, nasty bugs in Vista Beta 2 regarding write access to the public folder. These bugs will be fixed hopefully by the next public release. I will post another reply to you in a little while with instructions on how to get that to work right.
- JB

Network File and Printer Sharing
- Go to Control Panel -> Network and Internet -> Network File and Printer Sharing
NETWORK ACCESS: Change this to "Anyone who can connect to my network" if you would like other computers to access Vista without logging in.
Note: Even though this option says it is just for the public folder, it actually goes for all other shared folders and printers as well. (However, this does not bypass security; networked computers will be able to see all shared folders without logging on, but will not be able to access any resource unless it is set to allow guest or Everyone access)
PUBLIC FOLDER: Change this to (Reader) if you want to limit access to the Public folder to read-only. Change it to (Co-owner) if you want to allow full access.
PRINTER SHARING: If you want to allow access to your printers, select Allow.
*** IMPORTANT NOTE ***
If you set Network Access to "Anyone who can connect to my network" and have shared folders that allow write access, you must follow additional steps to get write access to work properly.
*These steps are necessary due to bugs in Windows Vista Beta 2, and should not be necessary in the future.*
Step 1:
- Click start - Type: cmd - Right-click cmd when it appears under Programs - Click run as administrator - If prompted for permission, click Continue - Type: net localgroup users guest /add - Press enter
Step 2:
- Click Start - Click Computer - Double-click on the drive with the windows logo in it (should be first one listed) - Right-click the Users folder - Click Share... - Click Advanced Sharing - If prompted for permission, click Continue - Make sure there is a checkbox next to "Yes, share this folder" - Click Permissions - Click Add - Type: Everyone - Press enter - Click the checkbox next to Full Control under Allow - Press OK - Press OK - Press OK
NOTE: If you were browsing your Vista computer when you made these changes, you may have to restart the computer you were browsing from to notice these changes.