DIRUSE from the 2003 Support Tools works well for getting folder size on a windows servers. http://www.microsoft.com/downloads/details.aspx?familyid=96A35011-FD83-419D-939B-9A772EA2DF90

For instance, the following command will display all directories over 300 MB in size:
diruse /S /M /Q:300 /D C:\

syntax;

DIRUSE displays a list of disk usage for a directory tree(s). Version 1.20

DIRUSE [/S | /V] [/M | /K | /B] [/C] [/,] [/Q:# [/L] [/A] [/D] [/O]] [/*] DIRS

/S      Specifies whether subdirectories are included in the output.
/V      Output progress reports while scanning subdirectories.  Ignored if /S i
 specified.
/M      Displays disk usage in megabytes.
/K      Displays disk usage in kilobytes.
/B      Displays disk usage in bytes (default).
/C      Use Compressed size instead of apparent size.
/,      Use thousand separator when displaying sizes.
/L      Output overflows to logfile .\DIRUSE.LOG.
/*      Uses the top-level directories residing in the specified DIRS
/Q:#    Mark directories that exceed the specified size (#) with a "!".
        (If /M or /K is not specified, then bytes is assumed.)
/A      Specifies that an alert is generated if specified sizes are exceeded.
        (The Alerter service must be running.)
/D      Displays only directories that exceed specified sizes.
/O      Specifies that subdirectories are not checked for specified size
        overflow.
DIRS    Specifies a list of the paths to check.

Note:   Parameters can be typed in any order. And the '-' symbol can be
        used in place of the '/' symbol.

        Also, if /Q is specified, then return code is ONE if any directories are
 found that
        exceed the specified sizes.  Otherwise the return code is ZERO.