If you're worried that you've been infected by the Flashback Trojan, the simple app Flashback Checker by independent developer Juan Leon checks for you.
If you don't feel comfortable using Terminal, just install Flashback Checker and click "Check for Flashback Infection". The app runs a simple script which will confirm whether you are infected or not. Note that it does not remove the Trojan. To ensure full removal, you must follow F-Secure's removal instructions which does require use of Terminal.
Remember that if you get the all clear, you must run Software Update on your Mac to ensure that the Java vulnerability is patched. If you're unsure, download the latest patched version of Java for Lion.
Flashback Checker is a simple way to check for the Flashback Trojan without having to use Terminal.