Slight correction to make. I replaced a 500 Meg stick with a 1Gb stick. The problem is sorted . It appears that although the two 1Gb sticks I bought on the net, despite the nice shiny stickers saying 1Gb, appear to be 500 meg sticks. I'm running the test now and will let you know the results. Thanks again
The computer had a 256Mb and a 512 Mb installed. I removed the 512 Mb stick and replaced it with what was supposed to be a 1Gb stick and it still read 768Mb. After running msconfig I replaced the 256Mb stick with the other 1Gb and when i ranmsconfig again maxmem read as 1Gb. Memtest 86 confirmed this. Life's a bitch. Again sorry to have wasted your time but the advice was gratefully received.