Just tried the 2.6.27-4-generic kernel, same problem, no network connection.

Also looks related to bug 240470.

uname -a
Linux pc-64 2.6.27-4-generic #1 SMP Mon Sep 22 04:40:15 UTC 2008 x86_64 GNU/Linux

lspci -vv
01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8101E/RTL8102E PCI Express Fast Ethernet controller (rev ff) (prog-if ff)
	!!! Unknown header type 7f
	Kernel driver in use: r8169
	Kernel modules: r8169

In messages file after trying to ping my router...

[   48.386666] [drm] Initialized drm 1.1.0 20060810
[   48.477882] pci 0000:00:02.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
[   48.477901] pci 0000:00:02.0: setting latency timer to 64
[   48.478458] [drm] Initialized i915 1.6.0 20060119 on minor 0
[   48.648550] r8169: eth0: link up
[   49.025233] NET: Registered protocol family 17
[  156.804031] ------------[ cut here ]------------
[  156.804044] WARNING: at /build/buildd/linux-2.6.27/net/sched/sch_generic.c:219 dev_watchdog+0x272/0x280()
[  156.804051] NETDEV WATCHDOG: eth0 (r8169): transmit timed out
[  156.804056] Modules linked in: xt_limit xt_tcpudp ipt_LOG ipt_MASQUERADE xt_DSCP ipt_REJECT nf_conntrack_irc nf_conntrack_ftp xt_state af_packet i915 drm ppdev cpufreq_userspace cpufreq_stats cpufreq_powersave cpufreq_ondemand freq_table cpufreq_conservative container video output sbs sbshc wmi pci_slot battery ac smsc47m1 smsc47m192 hwmon_vid i2c_i801 i2c_core lp snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm snd_seq_dummy serio_raw psmouse snd_seq_oss snd_seq_midi snd_rawmidi parport_pc parport snd_seq_midi_event snd_seq snd_timer snd_seq_device button iTCO_wdt iTCO_vendor_support snd soundcore snd_page_alloc intel_agp shpchp pci_hotplug evdev iptable_nat nf_nat nf_conntrack_ipv4 nf_conntrack iptable_mangle iptable_filter ip_tables x_tables ext3 jbd mbcache sg sd_mod sr_mod crc_t10dif cdrom ata_piix ata_generic pata_acpi libata scsi_mod dock r8169 uhci_hcd ehci_hcd usbcore thermal processor fan fbcon tileblit font bitblit softcursor uvesafb cn fuse
[  156.804216] Pid: 0, comm: swapper Not tainted 2.6.27-4-generic #1
[  156.804223] 
[  156.804224] Call Trace:
[  156.804232]  <IRQ>  [<ffffffff8024e83c>] warn_slowpath+0xbc/0xf0
[  156.804256]  [<ffffffff8026ac7f>] ? hrtimer_start+0xdf/0x1b0
[  156.804264]  [<ffffffff8026af51>] ? ktime_get_ts+0x61/0x70
[  156.804274]  [<ffffffff80246113>] ? hrtick_start_fair+0x173/0x190
[  156.804282]  [<ffffffff802462b7>] ? enqueue_task_fair+0x57/0x60
[  156.804289]  [<ffffffff8023c2b0>] ? enqueue_task+0x50/0x60
[  156.804297]  [<ffffffff80245d6d>] ? resched_task+0x2d/0x90
[  156.804307]  [<ffffffff802a6dc3>] ? ftrace_record_ip+0x173/0x290
[  156.804317]  [<ffffffff802126a4>] ? mcount_call+0x5/0x31
[  156.804325]  [<ffffffff803aa18a>] ? strlcpy+0x4a/0x60
[  156.804333]  [<ffffffff80494d72>] dev_watchdog+0x272/0x280
[  156.804340]  [<ffffffff8026cc2c>] ? sched_clock_cpu+0xcc/0x160
[  156.804350]  [<ffffffff80219d56>] ? read_tsc+0x16/0x40
[  156.804357]  [<ffffffff80494b00>] ? dev_watchdog+0x0/0x280
[  156.804365]  [<ffffffff80259f29>] run_timer_softirq+0x179/0x260
[  156.804374]  [<ffffffff80271484>] ? clockevents_program_event+0x54/0xa0
[  156.804383]  [<ffffffff80254c9c>] __do_softirq+0x8c/0x100
[  156.804391]  [<ffffffff802141ac>] call_softirq+0x1c/0x30
[  156.804398]  [<ffffffff802158a5>] do_softirq+0x65/0xa0
[  156.804405]  [<ffffffff80254a05>] irq_exit+0x95/0xa0
[  156.804413]  [<ffffffff802268e9>] smp_apic_timer_interrupt+0x89/0xc0
[  156.804421]  [<ffffffff802139b3>] apic_timer_interrupt+0x83/0x90
[  156.804425]  <EOI>  [<ffffffff8021ab92>] ? mwait_idle+0x52/0x60
[  156.804440]  [<ffffffff80210df7>] ? enter_idle+0x27/0x30
[  156.804447]  [<ffffffff80210e95>] ? cpu_idle+0x75/0x100
[  156.804455]  [<ffffffff80516525>] ? start_secondary+0x97/0xc2
[  156.804463] 
[  156.804468] ---[ end trace 45a2837ba317a2a8 ]---
[  157.628029] r8169: eth0: link up