Insufficient Memory

Dear Sir,
I have PIV 1.6 GHz with 256 MB RAM windows 98 se and office 2000 installed.
I connect to the Netware 3.12 server in lan. I use dos based programs too which are installed on server.
I am unale to work in two dos screens. Whene ever I open one application in commaned prompt it works fine. and kepping it open when i open another program in dos it says “Insufficient Memory”

What is the problem ?

Thanks