System crashing every morning

Every morning (UK time) when I wake up I find my system has 
crashed, normally at about 2am.  I looked at the log for the most recent 
one and ran it through ksymoops.  I'm quite a newbie so this doesn't 
mean much to me but does it mean anything to anybody here - in case 
you are wondering the system is an AMD K6-2 500Mhz, 128MB Ram, 
40Gb IDE Hard drive, Gigabyte GA-5VMM mobo.

Thanks in advance,
Alex Brett
[email protected]

Here's the output of ksymoops:

Apr  9 01:55:02 Server kernel: Unable to handle kernel NULL pointer 
dereference at virtual address 00000004
Apr  9 01:55:02 Server kernel: c0146f66
Apr  9 01:55:02 Server kernel: *pde = 00000000
Apr  9 01:55:02 Server kernel: Oops: 0000
Apr  9 01:55:02 Server kernel: CPU:    0
Apr  9 01:55:02 Server kernel: EIP:    0010:[prune_icache+54/304]    
Not tainted
Apr  9 01:55:02 Server kernel: EIP:    0010:[<c0146f66>]    Not tainted
Using defaults from ksymoops -t elf32-i386 -a i386
Apr  9 01:55:02 Server kernel: EFLAGS: 00010203
Apr  9 01:55:02 Server kernel: eax: 00000001   ebx: 00000000   ecx: 
c6a59ad8   edx: c6a59ac0
Apr  9 01:55:02 Server kernel: esi: c6a59ac0   edi: 00000000   ebp: 
c7783fa4   esp: c7783f88
Apr  9 01:55:02 Server kernel: ds: 0018   es: 0018   ss: 0018
Apr  9 01:55:02 Server kernel: Process kswapd (pid: 5, 
stackpage=c7783000)
Apr  9 01:55:02 Server kernel: Stack: 00000000 00000035 c592eac8 
c4d1f208 00000000 000000c0 000000c0 0008e000
Apr  9 01:55:02 Server kernel:        c0147087 ffffffcb 0000003f 
c012d613 00000000 000000c0 c146d130 000000c0
Apr  9 01:55:02 Server kernel:        000000c0 00000000 c7782000 
00000006 c012d695 000000c0 00000000 00010f00
Apr  9 01:55:02 Server kernel: Call Trace: 
[shrink_icache_memory+39/64] shrink_icache_memory [kernel] 0x27
Apr  9 01:55:02 Server kernel: Call Trace: [<c0147087>] 
shrink_icache_memory [kernel] 0x27
Apr  9 01:55:02 Server kernel: [<c012d613>] do_try_to_free_pages 
[kernel] 0x23
Apr  9 01:55:02 Server kernel: [<c012d695>] kswapd [kernel] 0x55
Apr  9 01:55:02 Server kernel: [<c0105000>] stext [kernel] 0x0
Apr  9 01:55:02 Server kernel: [<c0105726>] kernel_thread [kernel] 
0x26
Apr  9 01:55:02 Server kernel: [<c012d640>] kswapd [kernel] 0x0
Apr  9 01:55:02 Server kernel: Code: 8b 7f 04 8d 73 f8 8b 86 0c 01 00 
00 a9 38 00 00 00 74 19 68

>>EIP; c0146f66 <prune_icache+36/130>   <=====
Trace; c0147087 <shrink_icache_memory+27/40>
Trace; c012d613 <do_try_to_free_pages+23/50>
Trace; c012d695 <kswapd+55/f0>
Trace; c0105000 <_stext+0/0>
Trace; c0105726 <kernel_thread+26/30>
Trace; c012d640 <kswapd+0/f0>
Code;  c0146f66 <prune_icache+36/130>
00000000 <_EIP>:
Code;  c0146f66 <prune_icache+36/130>   <=====
   0:   8b 7f 04                  mov    0x4(%edi),%edi   <=====
Code;  c0146f69 <prune_icache+39/130>
   3:   8d 73 f8                  lea    0xfffffff8(%ebx),%esi
Code;  c0146f6c <prune_icache+3c/130>
   6:   8b 86 0c 01 00 00         mov    0x10c(%esi),%eax
Code;  c0146f72 <prune_icache+42/130>
   c:   a9 38 00 00 00            test   $0x38,%eax
Code;  c0146f77 <prune_icache+47/130>
  11:   74 19                     je     2c <_EIP+0x2c> c0146f92 
<prune_icache+62/130>
Code;  c0146f79 <prune_icache+49/130>
  13:   68 00 00 00 00            push   $0x0