OpenBSD boots on these machines; here's a dmesg (this is from an amd64 kernel, i386 works ok too).

OpenBSD 4.7 (GENERIC.MP) #128: Tue Mar  9 09:54:33 MST 2010
    deraadt@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP
real mem = 535625728 (510MB)
avail mem = 508928000 (485MB)
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 2.5 @ 0xfc410 (27 entries)
bios0: vendor American Megatrends Inc. version "V090L" date 12/19/2007
bios0: Intel SS4200-E
acpi0 at bios0: rev 2
acpi0: tables DSDT FACP APIC MCFG OEMB
acpi0: wakeup devices P0P2(S4) P0P1(S4) PS2K(S4) PS2M(S4) MC97(S4) P0P4(S4) P0P5(S4) P0P6(S4) P0P7(S4) P0P8(S4) P0P9(S4) USB0(S3) USB1(S3) USB2(S3) USB3(S3) EUSB(S3)
acpitimer0 at acpi0: 3579545 Hz, 24 bits
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: Intel(R) Celeron(R) CPU 420 @ 1.60GHz, 1600.24 MHz
cpu0: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,TM,SBF,SSE3,MWAIT,DS-CPL,TM2,CX16,xTPR,NXE,LONG
cpu0: 512KB 64b/line 2-way L2 cache
cpu0: apic clock running at 199MHz
ioapic0 at mainbus0: apid 1 pa 0xfec00000, version 20, 24 pins
acpiprt0 at acpi0: bus 0 (PCI0)
acpiprt1 at acpi0: bus 1 (P0P4)
acpiprt2 at acpi0: bus -1 (P0P5)
acpiprt3 at acpi0: bus 2 (P0P6)
acpiprt4 at acpi0: bus -1 (P0P7)
acpicpu0 at acpi0
acpibtn0 at acpi0: PWRB
pci0 at mainbus0 bus 0
pchb0 at pci0 dev 0 function 0 "Intel 82945G Host" rev 0x02
ppb0 at pci0 dev 28 function 0 "Intel 82801GB PCIE" rev 0x01: apic 1 int 16 (irq 10)
pci1 at ppb0 bus 1
em0 at pci1 dev 0 function 0 "Intel PRO/1000MT (82573E)" rev 0x03: apic 1 int 16 (irq 10), address 00:15:17:31:e4:d5
ppb1 at pci0 dev 28 function 2 "Intel 82801GB PCIE" rev 0x01: apic 1 int 18 (irq 11)
pci2 at ppb1 bus 2
sili0 at pci2 dev 0 function 0 "CMD Technology SiI3132 SATA" rev 0x01: apic 1 int 18 (irq 11)
scsibus0 at sili0: 2 targets
uhci0 at pci0 dev 29 function 0 "Intel 82801GB USB" rev 0x01: apic 1 int 23 (irq 5)
uhci1 at pci0 dev 29 function 1 "Intel 82801GB USB" rev 0x01: apic 1 int 19 (irq 3)
uhci2 at pci0 dev 29 function 2 "Intel 82801GB USB" rev 0x01: apic 1 int 18 (irq 11)
uhci3 at pci0 dev 29 function 3 "Intel 82801GB USB" rev 0x01: apic 1 int 16 (irq 10)
ehci0 at pci0 dev 29 function 7 "Intel 82801GB USB" rev 0x01: apic 1 int 23 (irq 5)
usb0 at ehci0: USB revision 2.0
uhub0 at usb0 "Intel EHCI root hub" rev 2.00/1.00 addr 1
ppb2 at pci0 dev 30 function 0 "Intel 82801BA Hub-to-PCI" rev 0xe1
pci3 at ppb2 bus 3
pcib0 at pci0 dev 31 function 0 "Intel 82801GB LPC" rev 0x01
ahci0 at pci0 dev 31 function 2 "Intel 82801GR AHCI" rev 0x01: apic 1 int 19 (irq 3), AHCI 1.1
scsibus1 at ahci0: 32 targets
sd0 at scsibus1 targ 0 lun 0: <ATA, GB0160EAFJE,> SCSI3 0/direct fixed
sd0: 381554MB, 512 bytes/sec, 781422768 sec total
ichiic0 at pci0 dev 31 function 3 "Intel 82801GB SMBus" rev 0x01: apic 1 int 19 (irq 3)
iic0 at ichiic0
adt0 at iic0 addr 0x2e: sch5027 rev 0x69
spdmem0 at iic0 addr 0x50: 512MB DDR2 SDRAM non-parity PC2-5300CL5
usb1 at uhci0: USB revision 1.0
uhub1 at usb1 "Intel UHCI root hub" rev 1.00/1.00 addr 1
usb2 at uhci1: USB revision 1.0
uhub2 at usb2 "Intel UHCI root hub" rev 1.00/1.00 addr 1
usb3 at uhci2: USB revision 1.0
uhub3 at usb3 "Intel UHCI root hub" rev 1.00/1.00 addr 1
usb4 at uhci3: USB revision 1.0
uhub4 at usb4 "Intel UHCI root hub" rev 1.00/1.00 addr 1
isa0 at pcib0
isadma0 at isa0
com0 at isa0 port 0x3f8/8 irq 4: ns16550a, 16 byte fifo
com0: console
pckbc0 at isa0 port 0x60/5
pcppi0 at isa0 port 0x61
midi0 at pcppi0: 
spkr0 at pcppi0
mtrr: Pentium Pro MTRR support
vscsi0 at root
scsibus2 at vscsi0: 256 targets
softraid0 at root
root on sd0a swap on sd0b dump on sd0b

nothing special is needed to read the sensors;

$ sysctl hw.sensors
hw.sensors.cpu0.temp0=46.00 degC
hw.sensors.adt0.temp0=16.00 degC (Remote)
hw.sensors.adt0.temp1=33.00 degC (Internal)
hw.sensors.adt0.temp2=36.00 degC (Remote)
hw.sensors.adt0.fan1=1297 RPM
hw.sensors.adt0.fan2=1352 RPM
hw.sensors.adt0.fan4=3932040 RPM
hw.sensors.adt0.fan5=3932040 RPM
hw.sensors.adt0.volt0=5.03 VDC (+5V)
hw.sensors.adt0.volt1=1.04 VDC (Vccp)
hw.sensors.adt0.volt2=3.32 VDC (Vcc)
hw.sensors.adt0.volt3=5.08 VDC (+5V)
hw.sensors.adt0.volt4=12.00 VDC (+12V)
hw.sensors.adt0.volt5=3.28 VDC (+Vtr)
hw.sensors.adt0.volt6=3.13 VDC (+Vbat)