I am trying to run a PowerShell script  from an SQL script.

Can you run shell commands from T-SQL? I don't know it that well. I do know however that you can run PowerShell stuff from within the management studio for SQL 2008. Probably in Agent jobs as well, although I've not tried.

I know that you can run PowerShell from management studio, but I was seeing if anyone knew the script to do so.

declare @svrName varchar(255)
declare @sql varchar(400)
--by default it will take the current server name, we can the set the server name as well
set @svrName = @@SERVERNAME
set @sql = 'powershell.exe -c "Get-WmiObject -Class Win32_Volume -Filter ''DriveType = 3'' | select name,capacity,freespace | foreach{$_.name+''|''+$_.capacity/1048576+''%''+$_.freespace/1048576+''*''}"'
--creating a temporary table
CREATE TABLE #output
(line varchar(255))
--inserting disk name, total space and free space value in to temporary table
insert #output
EXEC xp_cmdshell @sql

--script to retrieve the values in GB from PS Script output
select @@SERVERNAME as servername ,rtrim(ltrim(SUBSTRING(line,1,CHARINDEX('|',line) -1))) as drivename
,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
(CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0) as 'capacityGB'
,round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
(CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0)as 'freespaceGB',
round(100 * (round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('%',line)+1,
(CHARINDEX('*',line) -1)-CHARINDEX('%',line)) )) as Float) /1024 ,0))/
(round(cast(rtrim(ltrim(SUBSTRING(line,CHARINDEX('|',line)+1,
(CHARINDEX('%',line) -1)-CHARINDEX('|',line)) )) as Float)/1024,0)),0) as percentfree

from #output
--select * from #output
where line like '[A-Z][:]%'
order by drivename
--script to drop the temporary table
--drop table #output