Mixing RAM, will it work?

yes .

it will run at the speed of the slowest stick , but you are better off with the extra ram

yes ,

that will drop system performance a fraction , but the extra total of ram will more than compensate at the times your system needs it

Manually set the timings (especially the cas latency), and bus to that of the slower dimm (i.e the lowest bus speed and the highest (most lax) timings)..
However you may encounter stabilty issues due to the inability of one of your sticks to run at the voltage the bios set, so you may have to manually set the voltage to the higher one.
If you are lucky you may even be able to oc the 533 mhz one to reach 800 mhz or as close as possible by raising the voltage.
Honestly, does the bios of your laptop have these options? As far as I know most laptops don't allow the user to manually change speeds and voltages. If so you may just want to drop the additional dimm and see if it works!
What OS do you use? If you use windows XP and you don't game on this laptop, then 1 Gb is enough and slowing down your ram may slow down your whole system in certain situations. Windows vista, however, will make good use of the additional ram.
Hope that helped you.

What outlander_04 said.
Technically the faster stick will be downclocked to the speed of the slower stick, but the increased amount of RAM is going be way more beneficial and you will actually see an increase in system performance. With RAM, the most important thing is having enough. There is not a lot of difference in the speeds...as far as performance goes. You can only see the difference in benchmarks. Most people could not actually tell the difference between 333mhz DDR2 and 1333mhz DDR3 during normal PC daily tasks, and even gaming.... unless they ran a benchmark program.
There simply is not a huge difference.

DDR2 is so cheap, ditch it all and get 2x2gb

mixing is a hit and miss thing - never know what it will do, your better off with matched sticks etc

Ram golden rules - stick with most matched, and least possible ammount of sticks etc

Sure, if your budget is that tight.

I find Crucial to be over volted and prone to failure the past two years. They used to be good.

G.Skill, Corsair, Kingston, OCZ, Mushkin, all those are good, depends on which kit you pick.

Look for low voltage and low timings, like:

http://www.newegg.com/Product/Prod [...] 6820146764
OR
http://www.newegg.com/Product/Prod [...] 6820231219

Thats the main reason for the cheap RAM, lol. If I buy the EXACT same RAM it'll work in dual channel right?

Thanks for the help Proximon. I appreciate it.