Negotiation????

My classmates told me that I shouldn't tell them the true number, so the offer is far away from his number, but is $10,000 more than what I got from my previous company. This is a perm job. They asked me to sign the offer letter before March 25, 2010 and start the job on March 29, 2010. Could I send an email to the manager to negotiate a little bit more? I need to rent an aprtment there and can only come back on weekend.