Will upgrading my RAM increase boot time speed on Mac?

The others are most likely correct about the HDD being your biggest bottleneck. You have 4GB of RAM, and this is more than enough to boot from your HDD optimally. If you want to speed boot time up by installing RAM, you will really need to know what you're doing: You need a bootloader that will pick a minimal image of your OS up from a flash drive into RAM, and then boot from that image in RAM. It's possible, but the gains really aren't worth it.

If you find yourself turning the computer on and off all the time and this is effecting your productivity, perhaps you might wish to consider using the 'suspend' feature more often. I think you'll find that even with a slowish HDD you'll be happy with the response of resuming from a system suspend. Another little trick might be to optimize (defragment) your hard drive.

If I've been incapable of convincing you that you probably don't need an upgrade, by all means, buy a faster HDD! This most likely will improve your boot time. However, I hope you've managed to gather from this answer that your boot time shouldn't be the most significant cause for buying a hard drive. There should be other problems that you need to solve quickly before you bother buying a faster hard drive.

edit: It's also worth pointing out that adding RAM sticks that don't match the capacity of those already installed in your system will more likely slow things down! Try to buy sticks of RAM that are as close as possible (same make/manufacturer, if possible) to those you already have, unless you plan on replacing the whole configuration. The worst case scenario if you use entirely different sticks is you end up with a system that doesn't boot, or crashes all the time. I've had this happen to me, and it wasn't a pleasant experience.

A little bit but RAM increases performance more.

Buy a faster RPM hard drive to increase your boot up time. I'd recommend a Solid-State drive for extremely fast boot up!

the bottleneck in boot time is the hard drive, upgrade to a faster hard drive, the only time ram would be an issue during boot is if it started to fill up to the point it was almost full. and i know the mac os is not that bad...

If you want to boot faster (decrease boot time) then you want to upgrade to a faster hard drive.