Welcome to the MacNN Forums.

#1 would upgrading the ram void the warranty
#2 would 2.1 ghz 4g ram run photoshop,dreamweaver etc
#3 is the loud fan noise normal?

#1 No, unless you broke something inside while doing it
#2 Yeah
#3 Its fine, perfectly normal due to the design - Edit- it only does it when running loads of stuff (high cpu usage)

#1 No, but Apple will not support the RAM you install unless you purchase it from Apple. If you ever call them for hardware support, they will ask you to remove the non-OEM RAM and replace it with the original - so keep it.
#2 That's plenty of processor/RAM horse power. I use a 2ghz/2gig RAM Macbook for the same applications and they run perfectly.
#3 I don't think so, but that's a matter of personal preference.

thanks! one last question I noticed when I click finder underneath the shared tab there are a list of computers. How do I turn the share thing off?

Go into Finder-->Preferences-->Sidebar and uncheck any and all of the items under "Shared" that you don't want to see (in your case, probably "Bonjour Computers" but you might want to cut off "Connected Servers" as well just for good measure"