You can use of these variables...
The meaning of each variable is in the middle of the table
On the right side of the table are typical values which can be expected (however, real values may greatly differ)
NOTE: To get My Documents folder path, use USERPROFILE to get user profile dir and then add '\My Documents' to it

Variable

Meaning

Typical value

ALLUSERSPROFILE

Path to All Users folder

C:\Documents and Settings\All Users

APPDATA

Path to Application Data folder

C:\Documents and Settings\{username}\Application Data

COMPUTERNAME

The computer name set by the user

{computername}

COMSPEC

Path to cmd.exe

C:\Windows\System32\cmd.exe

HOMEDRIVE

The home drive

C:\

HOMEPATH

Path to the user folder WITHOUT drive

\Documents and Settings\{username}

PROGRAMFILES

Path to the Program Files directory

C:\Program Files

SYSTEMDRIVE

The drive containing the Windows XP root directory

C:\

SYSTEMROOT

The Windows XP root directory, usually

C:\Windows

TEMP and TMP

Path to temporary folder

C:\DOCUME~1\{username}\LOCALS~1\Temp

USERNAME

The User name

{username}

USERPROFILE

Path to user folder WITH drive

C:\Documents and Settings\{username}

WINDIR

Windows directory

C:\Windows