Taken from http://www.gearlive.com/news/article/psp_vs_ds_04011107/

Cost:
PSP - $250 (includes 32MB memory stick, headphones, AC adapter, carrying case, demo disc and wrist strap
DS - $150 (includes stylus, AC adapter and wrist strap)

Size:
PSP - 6.7 x .9 x 2.9 inches
DS - 5.9 x 1.1 x 3.3 (6 when open) inches

Weight:
PSP - .62 lbs
DS - .61 lbs

Screen Size:
PSP - 4.3 inch LCD - 16:9 ratio
DS - Two 3 inch LCDs - 4:3 ratio

Screen Resolution:
PSP - 480 x 272 pixels
DS - 256 x 192 pixels

Colors:
PSP - 16,800,000
DS - 260,000

Memory:
PSP - 32MB - 4MB DRAM (plus memory stick)
DS - 4MB

Media:
PSP - UMD - 1.8GB capacity
DS - Cartridge 1 gigabit (Note: 8 gigabits = 1 gigabyte, so PSP UMD discs hold about 14 x as much as the DS cartdridge)

Wireless:
PSP - IEEE 802.11b (Wi-Fi) up to 11Mbps - 16 players
DS - IEEE 802.11 (Wi-Fi) up to 2Mbps - 16 players

Battery Life:
PSP - 2.5 hours watching UMD movies - 3-6 hours playing games (depending on brightness and multiplayer function)
DS - 6-10 hours playing games

Features:
PSP - USB 2.0 port - Analog stick - JPG pics - MP3 music - MPEG4 video
DS - Touchscreen - Compatible with Game Boy Advance - Built in microphone

These are the facts. You decide.