Someone asked for a script that could delete previous versions for SharePoint 3.0. I don’t have a 3.0 dev environment but I do have a 2010 build and it interested me.

Function Delete-SPVersions ()
{
[CmdletBinding(SupportsShouldProcess=$true)]
param(
    [Parameter(Mandatory=$True)][string]$webUrl, 
    [Parameter(Mandatory=$True)][string]$listName, 
    [Parameter(Mandatory=$False)][string]$numberOfMajorVersions
    ) 

    #Get the web
    $web = Get-SPWeb $webUrl


    #Get the list
    $list = $web.Lists[$listName]

    $list.Items | % {
        #Get the item in a slightly more usable variable
        $item = $_

        Write-Output ("Deleting versions for item {0}" -f $item.Name)
        
        #Get all major versions
        #Note, the version ID goes up by 512 for each major version.
        $majorVersions = $item.Versions | ? { $_.VersionID % 512 -eq 0}

        #get the largest version number
        $latestMajorID = $majorVersions | select VersionID -ExpandProperty VersionID | sort -Descending | select -First 1

        #Slightly lazy way to get the latest major version and format it as a single point decimal
        Write-Output ("   Latest major version to retain is {0:0.0}" -f ($latestMajorID /512))
        
        #Filter the major versions to only those which are lower than the highest number - 512 * $numberOfMajorVersions
        $majorVersionsToDelete = $majorVersions | ? {$_.VersionID -le ($latestMajorID - 512 * $numberOfMajorVersions)}
        if ($majorVersionsToDelete)
        {
            $majorVersionsToDelete | % {
                Write-Verbose ("  Deleting major version {0}" -f $_.VersionLabel)
                if ($pscmdlet.ShouldProcess($_.VersionLabel,"Deleting major version"))
                {
                    $_.Delete()
                }
            }
        }
        else
        {
            Write-Verbose "No major versions to delete"
        }
        
        #Re-fetch the item to ensure that the versions are still valid
        $item = $list.GetItemByUniqueId($item.UniqueId)
        
        #Get all the minor versions
        $minorVersions = $item.Versions | ? { $_.VersionID % 512 -ne 0}

        #Delete Minor versions greater than the last major version kept
        $minorVersionsToDelete = $minorVersions | ? {$_.VersionID -lt $latestMajorID}
        if ($minorVersionsToDelete)
        {
            $minorVersionsToDelete | % {
                Write-Verbose ("Deleting minor version {0}" -f $_.VersionLabel)
                if ($pscmdlet.ShouldProcess($_.VersionLabel,"Deleting minor version"))
                {
                    $_.Delete()
                }
            }
        }
        else
        {
            Write-Verbose "No minor versions to delete"
        }
    }
    $web.Dispose()
}