[RESOLVED]Fetch email just like referral id from url in register form??

[nirvana43]

Hello
Can anyone tell me how can i get email address field on register form, from url?
Just like referral link i.e. http://www.myforum.com/register.php?referrerid=10
I will be generating links as http://www.myforum.com/register.php?referrerid=10&email=username@email.com
What i wanna do is, just like referralid is taken from url and set in referral field of register form, i wanna take email from url and set it on the filed in register form.
Now i have already done customization till register link with referral id and email generation.
All i wanna know is, how do i catch email id from url...
I mean which files i'm suppose to edit?
And yeah there is "Agree to Forum Rules" thing before registration form actually appears (And i know vbulletin uses cookies to get referral id from actual link or something like that). so please tell me how do i add email to this system?

Detailed instructions are strongly appreciated and helper will get full credits.