2gb RAM recognized as 3gb?

[RlxdN10sity]

I recently installed 3 x 1GB PC2100 DDR 266MHz RAM modules in my old machine. It made a rapidly repeating beep on POST. I shut it down took out one of the modules and fired it back up. With only 2 x 1GB modules installed machine boots and runs fine but shows that 3gb have been installed when I view My Computer Properties.
What is causing this?

OS = WinXP Pro SP3

Mobo documentation says:
"184-pin DDR SDRAM module socket x3"
"Support 2 pcs. DDR333 or 3 pcs. DDR200/DDR266 DDR SDRAM Modules"
"Expandable to 3.0GB"

 

[RlxdN10sity]

Anyone?