There are many reasons for that, one could be your security (antivirus) program is doing some type of scan as you open the program(s).  Even with 2GB of RAM that isn't a huge amount for Vista and depending on how many programs you have open that could be an issue. If you open a program that is dependent on the internet, it can go "not responding" until it has an Internet connection or response from a remote server.  If you have a P2P program installed that could very well be the problem as potentially your PC can be infected with malware, spyware, etc.

The memory is most likely not compatible and if it worked it would slow down your system as it would be slower bus speed memory. 

 

I have three PC's, two desktops and a laptop all running Vista Home Premium 32 bit and the one that was upgraded from XP runs better and faster than it did with XP.  The only issue is the Vista "nags" when you try to do some functions. 

 

Since you run antivirus scans (make sure the antivirus program is up to date and the virus data file is up to date).  Also run a spyware program such as Spybot to check for spyware, malware, etc.

Thanks for the suggestions fireberd. Some of what you say may be true although I do not have a P2P program running right now. Also frequently I AM connected to the internet but this 'Not Responding' can kick in at any time, sometimes one right after another. I do not like Vista OS and have had so much trouble in the 3 mos I have had this new Dell computer. I try to keep Startup applications to a minimum. Also run anti-virus programs frequently. Maybe I should increase the RAM. I still haven't junked my old Dell computer...a Dimension 2400...do you think I could salvage one of the two 500MB Ram cards before I junk it and install it in the Inspiron 530? I have a slot open. Is that possible?

I have a Dell E-520 with Vista Home Premium and 2 gig memory 180 HD, and have never had a problem. If you have Vista  Home Premium I don't think it will recognize over 3 gig of memory anyway but not am sure of this.

Russ