Hi
asrock are correct when a motherboard says it can handle upto 2gb ram but as you know 1gb ram = 1024mbs so two of then takes it over the 2 gb that the board can support on pc3200 400mhz, it will support 2 gbs of the lower memory ie pc2700. or lower. also the motherboard you have runs at 800fsb and with your pentium it should run ok. going back to the unstable part it maybe that the thermal compond between your heatshink and processor may not be good enough, you have to cover the whole top of the processor to keep the temp down as I found out with mine.
here is the tech stuff.
Product Type Mainboard
Form Factor Micro ATX
Width 24.4 cm
Depth 20.3 cm
Compatible Processors Celeron, Pentium 4
Processor Socket Socket 478
Chipset Type VIA UniChrome P4M800
Max Bus Speed 800 MHz
BIOS Type AMI
Storage Controller ATA-133, Serial ATA-150 (RAID)
Power Connectors 4-pin ATX12V connector, 20-pin main power connector
Processor
Installed Qty (Max Supported) 0 ( 1 )
Memory
Supported RAM Technology DDR SDRAM
RAM Installed ( Max ) 0 MB / 2 GB (max)
Supported RAM Speed PC2100, PC2700, PC3200
Video
Graphics Controller VIA UniChrome P4M800
Video Memory Shared Video Memory (UMA)
Audio
Audio Output Sound card
Audio Codec CMI9761
Sound Output Mode 5.1 channel surround
Compliant Standards AC '97
Telecom / Networking
Networking Network adapter - Ethernet, Fast Ethernet
Features
BIOS Features ACPI support, SMBIOS 2.3.1. support, Hyper-Threading Technology
Hardware Monitoring CPU core temperature, chassis temperature, CPU fan tachometer, chassis fan tachometer, system voltage, CPU overheating protection
Sleep / Wake Up Wake on LAN (WOL)
Expansion / Connectivity
Expansion Slots Total (Free) 3 PCI
1 AMR
1 AGP 8x ( 1.5 V )
1 processor - Socket 478
2 memory - DIMM 184-PIN
Storage Interfaces Serial ATA-150 - connector(s): 2 x 7pin Serial ATA - RAID 0 / RAID 1 / JBOD
ATA-133 - connector(s): 2 x 40pin IDC - 4 Device(s)
Interfaces 1 x network - Ethernet 10Base-T/100Base-TX - RJ-45
1 x storage - floppy interface - 34 PIN IDC
1 x keyboard - generic - 6 pin mini-DIN (PS/2 style)
1 x mouse - generic - 6 pin mini-DIN (PS/2 style)
6 x Hi-Speed USB - 4 PIN USB Type A
1 x parallel - IEEE 1284 (EPP/ECP) - 25 pin D-Sub (DB-25)
1 x display / video - VGA - 15 pin HD D-Sub (HD-15)
1 x audio - line-In - mini-phone stereo 3.5 mm
1 x audio - line-out - mini-phone stereo 3.5 mm
1 x audio - input - mini-phone 3.5mm
Additional Connectors (Optional) 2 x Hi-Speed USB
Miscellaneous
Cables Included 1 x Serial ATA cable
1 x floppy cable
1 x IDE cable
Software Included Drivers & Utilities
Compliant Standards Plug and Play, ACPI, CE, WHQL, FCC
hope this helps a little.