Just as you can setup the Subversion client to not prompt for a password every time you communicate with the Subversion server in a similar but not so secure way you can do this with TortoiseSVN.
The easiest way to do this is to right click in Windows Explorer, select Tortoise > Settings. Then in the Settings window select Network. Then in the SSH client set use the Tortoise SSH client, TortoisePlink, to use your username and password. For example:
D:\TortoiseSVN\bin\TortoisePlink.exe -l foo -pw bar