How do I find out if there is an empty memory slot without opening up the PC.?

I don't mind downloading 3rd party tools but I don't want to install (tools that will run not install)
Answers:
First of all you should know (via motherboard user manual, you can download if you dont have it handy) how many slots are on the MB

then go to this page http://www.cpuid.com and download a program called CPU-Z (dont need to install, it runs directly from the downloaded ZIP file)

click on the memory tab and you can then select Slot1, slot2..



hope this helps.
try the following, they are terriffic
http://www.windowsbbs.com/index.php.
Read your motherboard's instruction manual and see how many memory slot does the mainboard have. Now start your computer and see what the POST result is saying about the ram (it should display the amount of RAM in each slot). Knowing how many RAM slots are on the motherboard (from the manual) and how many of them are used (from the POST result), it's easy to find out if there are any free memory slots on the mainboard.
this is the tool youll need http://belarc.com/free_download.html.
this thing is great it will tell you everything about your pc i mean everything. inside hardware if you have all your updates if your on a network how many dirves you have even network drives. between download and running it only takes maybe 5 mins before you have all the info you want. good luck
when booting up the post screen may say how many banks for memory you have, and how many are populated.
manuals are not always helpful as they may not actually include specific support for your board (similar model different revision number may be shown)

sorry but the easiest way is to open the machine.
Download PC wizard 2006, it tells about you ur system inside out. It details what is on your motherboard,thus should tell you how many memory channels are empty on your motherboard.
I had used this software sometime ago now, but I think that it does show the channels free.
Not sure if you can do it remotely, but if you go to www.crucial.com, you can download a small program from them which tells you your exact configuration and recommends memory modules to suit.

Hope this helps ......
go to download.com and search for belarc advisor ,run it and it will give you the full specs of your comp
A good site to try for what you're asking is:

http://www.crucial.com/index.asp.

If you know what motherboard you have, on the first page use the Crucial Memory Advisor. If you're willing to download a small program from Crucial you can use their Crucial System Scanner (further down that first page). I have used both methods, and installing the Crucial system scanner software doesn't appear to install any spyware or malware. It also appears to be accurate. It indicates which slots are used, which are free, and what type of memory would be suitable for your computer.

Best of luck.
Simple, go to your device Manager and look at the installed hardware you've got!