WMA stands for Windows Media Audio, and is therefore incompatible with the iPad. If you just wanted to remove the attachment for use elsewhere, I would recommend something like Dropbox. Get the free app and set up an account. Once set up, and the Dropbox app is linked to your Dropbox account, you can hold the attachment until the menu pops up and select Open with... Dropbox will be an option.
Once the file is in your Dropbox, you can get the PC/Mac app so that you can access these files from your desktop.
There may be a player in the app store that will play the WMA file, but the native apps will not.