I have an HTC desire and am running out of storage space. How do i install an app directly to my SD card?

[AtlasUltimate]

How do I switch the download location for the Google play store to my sd card?

 

[Titillating]

You can't. This is no longer a function supported by official versions of Android. The only way to get around this is to root your device, which opens up a whole other can of worms.