Weight
Although the PSP 2000 is slimmer than the PSP 1000, the difference in weight is easily recognized. The system weighs about 1/3 less than its predecessor.
UMD Port
There is a change to the way Universal Media Disks are put in the PSP. Instead of sliding something that pops open, the UMD port can be pulled open in the PSP 2000.
USB Charge
As of firmware upgrade 3.6, the PSP 2000 can charge the battery through its USB cable. This is not possible for the PSP 1000.
RAM Upgrade
The Random Access Memory of the PSP Slim is doubled. It is 64 megabytes. This was done to lower the loading time of games.
W-Lan Switch
The switch for the PSP to connect to a Wi-Fi is in a different spot. Unlike the PSP 1000 which has the switch on the left side, the switch is on the top of the PSP 2000.