If you want to use the NET USE command to map drives, you need to either get rid of spaces in your UNC path or enclose the UNC path in quotation marks:
NET USE U: "\\Win2k3-svr-bd1\Users\Ian Taylor"
But if you're using a Windows NT/2000/XP workstation to log on to a domain, you shouldn't need to use a logon script to map a home directory. You can define a home directory in Active Directory Users and Computers (ADUC). Double-click a user in ADUC and go to the Profile tab. Under the "Home Folder" section, you can define a drive mapping.