you can store your userid and psw in config file i.e. OWSTIMER.EXE.CONFIG. you can find this file at C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN.
if it is not their then you can create one. please make sure that file name must be in capital leters. below i have mentioned sample content of this config file.
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add key="USERID" value="testUser" />
<add key="PSW" value="testPSW" />
</appSettings>
</configuration>
if you are using C# then you can access these nodes using
System.Configuration.ConfigurationManager.AppSettings["USERID"]
System.Configuration.ConfigurationManager.AppSettings["PSW"]
Dont forget to reset your sharepoint timer service once you made changes in your config file.