Is it safe?

Well yes, considering you know the person and the work is vital at the moment. But after the work completes change the password.

ok, considering that i don't know the person, then, is it possible for him to misuse it, for his own cause?

I do we can misuse it but How ?

^^^err....dint get your question buddy...are u asking wat i asked?

I think it would be safe.The other guy isn't going to gain anything by messing up your internet settings except your choiciest swear words..

But yup,as QwertyManiac said change your password after the configuration is over.Or even better do the configuration yourself.

A wild guess : u r not working for CIA, FSB or for that matter RAW. And assuming that ur system does not store "state secret", but only personal secrets, it is "probably" safe.

But do change your password later on.

Well yes, he can steal your ID/Pass stored in the router to be basic ( in malicious terms, I've done this myself, its a noobie job ). And then cause he can access your router, there is no stopping him from harming your computer cause that's where the Download/Upload takes place from.

thanks.....err...the situation is something like, i want to allow him to access my server just for once, but he has not been able to do that, as port 80, the default port number for the server, is blocked....

but i am not able to find out where actually it is blocked..hence i thought it might have been blocked in the modem configuration... still am not able to figure it out...

You have to add 80 to the forwarded ports list and unblock it for all connections via the software firewall. It'll definitely work then. Unless the ISP has restricted it or some higher surface block.

err...."via the software firewall"--> is this the router firewall's WAN access? do i need to enable WAN access?