Windows 7: How do I encrypt my HDD? And also need more help.

Hello, I am a new user here, I have a two HDDs.
I want to know the procedure for encrypting my hdd. Here are also few things that I also want to know:
1. If i do encryption on my hdd, can a virus/malware/Trojan affect that HDD or not.
2. Also if i do encryption can I download things from internet on that hdd.
3. If I install windows 7 on encrypted HDD and install other programs or games on other HDD, then it will work or not. I think this will ensure security for windows 7 and less chance of being affected.



Please let me know these will work or not. If there is any other method please tell me.


THANKS IN ADVANCE.

1-Yes it can
2-yes you can
3-usually yes

BUT

If you lose the key, if a single bit of the key becomes corrupt, you will lose everything. IMHO it is just not worth it!

Thats mean virus can affect encrypted HDD.
But I don't understand what you mean by this I also want to know which software is good for encryption of HDD.

TrueCrypt (TrueCrypt - Free Open-Source On-The-Fly Disk Encryption Software for Windows 7/Vista/XP, Mac OS X and Linux) is an excellent encryption app that handles volume files and partition/disk-based encryption. It will encrypt your system partition on the fly as well. While it's true that losing your password will prevent any and all access to the encrypted data (since there's no backdoor of any kind), possible data corruption due to errors is limited to one HD sector at a time, and Truecrypt offers (actually forces you) to write a rescue CD with the volume key and encryption headers that are specific to your system. But again, you must remember the password you choose - without it, even the rescue CD will be useless (which is by design).
But to say that one single corrupted bit will make the entire volume useless is not correct.

Edit: Obviously malware can affect any encrypted volume just like any regular volume as long as the encrypted one is mounted and visible to your system. But once dismounted, it will just show up as a 'raw' (unformatted) partition - the data could still be deleted or destroyed but nothing can be read and stolen from it.

THanks Corazon and zigzag 3143 for solving my problems. Thanks again.