I have the same: NetworkManager uses 100% CPU and does not connect (the "Connecting" logo keeps animating), on a Lenovo Thinkpad T61 running Hardy Beta x86_64:

$ uname -a
Linux nl-l3a9355 2.6.24-12-generic #1 SMP Wed Mar 12 22:31:43 UTC 2008 x86_64 GNU/Linux

$ dpkg -l | grep network-manager
ii  network-manager                            0.6.6-0ubuntu2                network management framework daemon
ii  network-manager-gnome                      0.6.6-0ubuntu1                network management framework (GNOME frontend

$ sudo lspci -vv
03:00.0 Network controller: Intel Corporation PRO/Wireless 4965 AG or AGN Network Connection (rev 61)
	Subsystem: Intel Corporation Lenovo ThinkPad T61
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR+ <PERR-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 505
	Region 0: Memory at df3fe000 (64-bit, non-prefetchable) [size=8K]
	Capabilities: [c8] Power Management version 3
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
		Status: D0 PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [d0] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable+
		Address: 00000000fee0300c  Data: 41b9
	Capabilities: [e0] Express Endpoint IRQ 0
		Device: Supported: MaxPayload 128 bytes, PhantFunc 0, ExtTag-
		Device: Latency L0s <512ns, L1 unlimited
		Device: AtnBtn- AtnInd- PwrInd-
		Device: Errors: Correctable- Non-Fatal- Fatal- Unsupported-
		Device: RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop+
		Device: MaxPayload 128 bytes, MaxReadReq 128 bytes
		Link: Supported Speed 2.5Gb/s, Width x1, ASPM L0s L1, Port 0
		Link: Latency L0s <128ns, L1 <64us
		Link: ASPM L0s Enabled RCB 64 bytes CommClk+ ExtSynch-
		Link: Speed 2.5Gb/s, Width x1

part of /var/log/syslog:

Mar 22 10:07:36 nl-l3a9355 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) complete. 
Mar 22 10:07:36 nl-l3a9355 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) starting... 
Mar 22 10:07:36 nl-l3a9355 NetworkManager: <info>  Activation (wlan0/wireless): access point 'Jesper-WiFi' is encrypted, and a key exists.  No new key needed. 
Mar 22 10:07:37 nl-l3a9355 NetworkManager: <WARN>  nm_signal_handler(): Caught signal 11.  Generating backtrace... 
Mar 22 10:07:37 nl-l3a9355 NetworkManager: ******************* START **********************************
Mar 22 10:07:38 nl-l3a9355 NetworkManager: (no debugging symbols found)
Mar 22 10:07:38 nl-l3a9355 NetworkManager: Using host libthread_db library "/lib/libthread_db.so.1".
Mar 22 10:07:38 nl-l3a9355 NetworkManager: (no debugging symbols found)
Mar 22 10:07:38 nl-l3a9355 last message repeated 10 times
Mar 22 10:07:38 nl-l3a9355 NetworkManager: [Thread debugging using libthread_db enabled]
Mar 22 10:07:38 nl-l3a9355 NetworkManager: [New Thread 0x7f40d74b0780 (LWP 5133)]
Mar 22 10:07:38 nl-l3a9355 NetworkManager: [New Thread 0x422c9950 (LWP 5567)]
Mar 22 10:07:38 nl-l3a9355 NetworkManager: [New Thread 0x414e2950 (LWP 5510)]
Mar 22 10:07:38 nl-l3a9355 NetworkManager: (no debugging symbols found)
Mar 22 10:07:38 nl-l3a9355 last message repeated 9 times
Mar 22 10:07:38 nl-l3a9355 NetworkManager: 0x00007f40d581fcc6 in poll () from /lib/libc.so.6
Mar 22 10:07:38 nl-l3a9355 NetworkManager: ******************* END **********************************