I was having a similar problem here:
https://forums.macrumors.com/threads/384121/
To connect to the windows machine, I had to click "Go-->go to server" in the finder (or just hit

+k). Here I would type in the IP address of the windows machine. It would pop up asking for a user name and password, but I generally found I could type just about anything and it would connect. On the windows machine, I made sure file sharing was turned on and that specific folders were checked for sharing.
In terms of transferring from the mac, first you need to create an account on the mac that has the same user name and password as the windows user account. Afterwords, in the mac, go to a specific folder (for example, I did my music folder) and click "get info". From here, first make sure "shared folder" is checked. At the bottom, under sharing and permissions, click the + sign, then select the new user account (the one that matches your windows machine). Make sure to set that person to "read and write". Finally, (and this is the really important part for getting rid of the permissions error), click on the gearbox (to the right of the -) and select apply to enclosed items.
That should do the trick. On the windows machine, go to run and type: \\ipaddress where ip address is the ip of the Mac. If you are running Vista, it will authenticate based on your current log in (hence why you need the new account). If you are on XP, it should ask you for a name and password, so enter the name and password for the new account.
Good luck
EDIT: Also, just to make sure you have the settings right, make sure in "sharing" that you are using the "connect using smb" option checked. When you do this, it will tell you the ip address the windows machine needs to use to connect (aka your current IP)