Yes, it will. A lot longer.
A standard VGA image (640×480) or SDTV video frame is a mere 0.3 megapixels whereas a standard 720p frame (1280×720) is about 0.9MP (three times the size) and 1080p (1920×1080) is just over 2MP, or almost seven times as large. That right there means that something that takes a few hours in standard definition will take days in 1080p.
Also, your CPU isn’t nearly as fast as an i3; a mere 1,619 according to PassMark . By comparison, my $500 desktop (an i3–530) posts a 2,729 and according to this your 9400M graphics chip gets a mere 140 compared to the 333 of my Toshiba T135, the 775 of my desktop’s low-end budget card, or the blazing performance of many mid-range desktop cards in the $150 range. That doesn’t count the fact that you only have 256MB of VRAM either.
My point is that it’s technically possible to edit HD video on your current rig, bit it will be ssslllooowww. There are some things that really are best done on a desktop system, and I would skip any iMac with a Core2 Duo as even the lowest of the i-series CPUs will eat it’s lunch and the iMacs that use Core2s also use a 9400M or worse GPU. If upgrading to a newer Macbook or getting a current-gen iMac isn’t an option, you can still edit things, but prepare to leave your laptop unattended for a few days at a time while it processes.