First of all I'm sorry to hear that you are having problems upgrading your memory.
I have had a look in to this system and it can support up to 1GB of memory in a single slot. When installing new memory it can sometimes look like it's fully installed but it needs to be pressed in harder. I would try the new memory again but making sure that it's installed correctly. Sometimes older memory goes in quicker so it could be down to the memory not being installed correctly.
You said that you have ordered additional RAM, did you order it from Crucial? If so can you confirm the part number of the memory you have ordered? It will be printed on the label on the memory and look something like "CT12864X335.16FFY"
You can see all the memory we recommend for this system HERE. Please let us know how it goes and if you need any further help we would be more than happy to help.