RAM Increase ... What to Do

I am not a novice but never paid any attention to RAM memory. I have no idea what the types are or what does what.

So, I need assistance.

I will be upgrading soon to Windows7 home 64-bit.

I have a Dell Vostro 420 with the following memory: 4GB Dual Channel DDR2 SDRAM 800MHz 4 DIMMs

I want to increase the amount of memory from the current 4GB to at least 8GB (with the ability to increase to 16GB).

Obviously, I want the same efficiency, etc as the currently installed memory but if it is possible to upgrade that effectiveness then that is great.

Any ideas and/or suggestions aremost welcomed.

Thanks.

What CPU do you have? Do you know the motherboard?

There's a good chance that your machine can support x64, but Dell may not provide support. Check out the Dell support forums. There's a number of folks who have gone through the change themselves, many looks like they had to do their own leg work. For example:
http://en.community.dell.com/forums/t/19255828.aspx
http://en.community.dell.com/forum [...] 94897.aspx
http://en.community.dell.com/forum [...] 95732.aspx

Why do you want to jump to 8GB RAM? You mention you don't know what types are or what does what. 8GB could easily be overkill for you, depends on what you use the machine for.