Another answer I posted to the NG, and not all that hard once you know the right classes to use from the BCL. But if you didn't know where to look, I can imagine it being a royal pain in the ass.

--- begin ConvertTo-Sid.ps1 ---

param ($account = $(throw "need account in form domain\username or
[ntaccount] object"))

if ($account -is [security.principal.ntaccount]) { 
    $ntaccount = $account

} else {
    $ntaccount = new-object security.principal.ntaccount $account

}

$ntaccount.translate( [security.principal.securityidentifier] )

param ($sid = $(throw "need sid string or [securityidentifier] object"))

if ($sid -is [security.principal.securityidentifier]) {
    $securityidentifier  = $sid

} else { 
    $securityidentifier  = new-object security.principal.securityidentifier $sid

}

$securityidentifier.translate( [security.principal.ntaccount] )

--- end ConvertTo-NTAccount.ps1 ---

You can pass strings as args, or their respective native objects. They both output objects. The output of one can be used as the input of the other.

Then get ready for PS+ !

http://www.powershell.com/plus/

I got tired of typing add-pssnapin blah, especially with Quest's AD snap-in's longer than usual name so I came up with a little script that enumerates registered snap-ins, and lists a simple numbered menu showing those that are not already loaded into memory. You just type the number and hit enter to load it. Enter on an empty line exits the script. Yeah, it's brain-dead, but hey, I think I was brain-dead to continually type long commands in every single session to load stuff  

UPDATE 2007-08-16: I was even more braindead than I realised - I copied up a broken version without the $notloaded array. Ooops. Fixed.

1. write-progress "Enumerating Snapins" "Registered..."
2. $snaps = get-pssnapin -r
3.  
4. write-progress "Enumerating Snapins" "Loaded..."
5. $loaded = get-pssnapin | % {$_.name}
6. $notloaded  = @()
7.  
8. write-progress "Enumerating Snapins" "Complete." -Completed # glitchy
9.  
10. $i = 0; "";
11.  
12. foreach ($snap in $snaps) {
13.         if (-not($loaded -contains $snap.name)) {
14.                 Write-Host -fore cyan -nonewline "${i}) "
15.                 write-host -fore green $snap.name
16.                     $notloaded  += $snap
17.                 $i++
18.         }
19. }
20.  
21. if ($i -eq 0) {
22.         Write-Warning "Any eligible snapins are already loaded."
23.         exit;
24. }
25.  
26. $i--;
27. Write-Host -fore yellow "<enter> to quit"
28.  
29. do {
30.         write-host -nonewline "Load 0 - ${i}: ";
31.         $choice = [console]::readline()
32.         if ($choice -and ($choice -lt 0) -or ($choice -gt $i)) {
33.                 Write-Warning "'${choice}' is out of range!"
34.                 continue;
35.         }
36.         if ($choice) {
37.                 "loading $($notloaded[$choice].name) ..."
38.                 add-pssnapin $notloaded[$choice]
39.         }
40. } while ($choice)

Just pop it into a function or a ps1 script.

You'll notice how when this is run from a clear screen, the progress bar disappears, then suddenly reappears and the first few menu items are hidden. This is a bug in the powershell.exe host. Vote on it here:

https://connect.microsoft.com/feedback/ViewFeedback.aspx?FeedbackID=291380&SiteID=99

Someone on the PowerShell NG asked recently if there was some kind of equivalent to c#'s "using namespace;" or VB.NET's "Imports namespace" statements. Well, the short answer to that is no, not really. However, you can simulate it by creating functions for each static method on the class:

1. param([type]$type = $(throw "need a type!"))
2.  
3. $type | gm -static | ? {$_.membertype -eq "method" } | % {
4.         $func = "function:$($_.name)"
5.         if (test-path $func) { remove-item $func }
6.         $flags = 'Public,Static,InvokeMethod,DeclaredOnly'
7.         new-item $func -value "[$($type.fullname)].InvokeMember('$($_.name)', ${flags}, `$null, `$null, `$args[0])"
8. }

Save this as "import.ps1" for example and use like so:

PS > . .\import.ps1 ([Math])
...

PS > Sin 1
0.841470984807897

Methods that take multiple args must have them passed as a single array:

PS > Max @(1,2)
2

Have fun!

Update: there are some interesting extensions appearing based around my initial post on microsoft.public.windows.powershell.