My brother fixed it...
Before you do anything else, you should try to back up your data disk if there's anything important. You may need to take it out of the computer and put it an external housing. If nothing else, you should be able to grab important files from the Windows side.
Anyhow, here's how we fixed it:
From Windows, go to Start/Run... (or Windows-R {Command-R}) and run DISKPART
This is the Microsoft disk partition utility.
Type "list disk" to show your disks:
<pre style="background-color: #eee">
DISKPART> list disk
Disk ### Status Size Free Dyn Gpt
----=--- ----=----=--- ----=-- ----=-- --- ---
Disk 0 Online 233 GB 0 B
Disk 1 Online 596 GB 127 MB *
Disk 2 Online 931 GB 128 MB
</pre>
The GPT volume is probably your Mac disk; let's look at it:
<pre style="background-color: #eee">
DISKPART> select disk 1
Disk 1 is now the selected disk.
DISKPART> list part
Partition ### Type Size Offset
----=----=--- ----=----=----=- ----=-- ----=--
Partition 1 System 200 MB 20 KB
Partition 2 Primary 595 GB 200 MB
DISKPART> select part 2
Partition 2 is now the selected partition.
DISKPART> detail part
Partition 2
Type : ebd0a0a2-b9e5-4433-87c0-68b6b72699c7
Hidden : No
Required: No
Attrib : 0000000000000000
Offset in Bytes: 209735680
Volume ### Ltr Label Fs Type Size Status Info
----=---=- --- ----=----=- ---=- ----=---=- ----=-- ----=---- ----=---
* Volume 2 E Macintosh H HFS Partition 595 GB Healthy
</pre>
OK, we know we have the right partition, but the type isn't right (that ID is for a "Basic Data Partition"). DISKPART has the SETID command, but it won't work, so we'll use GPT FDISK for Windows. Get it at:
[http://sf.net/projects/gptfdisk>
extract and run as administrator (gdisk.exe)
<pre style="background-color: #eee">
GPT fdisk (gdisk) version 0.6.5
**********************************************************************
Most versions of Windows cannot boot from a GPT disk, and most varieties
prior to Vista cannot read GPT disks. Therefore, you should exit now
unless you understand the implications of converting MBR to GPT, editing
an existing GPT disk, or creating a new GPT disk layout!
**********************************************************************
Are you SURE you want to continue? (Y/N): y
Type device filename, or press <Enter> to exit: 1:
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
</pre>
Print the partition table to make sure we're in the right place:
<pre style="background-color: #eee">
Command (? for help): p
Disk 1:: 1250263728 sectors, 596.2 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 00001494-45A0-0000-923B-0000AC4A0000
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1250263694
Total free space is 262157 sectors (128.0 MiB)
Number Start (sector) End (sector) Size Code Name
1 40 409639 200.0 MiB EF00 EFI system partition
2 409640 1250001543 595.9 GiB 0700 Customer
</pre>
And get detailed information:
<pre style="background-color: #eee">
Command (? for help): i
Partition number (1-2): 2
Partition GUID code: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (Linux/Windows data)
Partition unique GUID: 000043C0-3EEC-0000-B927-000090380000
First sector: 409640 (at 200.0 MiB)
Last sector: 1250001543 (at 596.0 GiB)
Partition size: 1249591904 sectors (595.9 GiB)
Attribute flags: 0000000000000000
Partition name: Customer
</pre>
OK, let's change the GUID code:
<pre style="background-color: #eee">
Command (? for help): t (change partition code)
Partition number (1-2): 2
Current type is 'Linux/Windows data'
Hex code (L to show codes, 0 to enter raw code, Enter = 0700): af00
Changed type of partition to 'Apple HFS/HFS+'
</pre>
Now verify that it is the right ID (the same one as in the article):
<pre style="background-color: #eee">
Command (? for help): i
Partition number (1-2): 2
Partition GUID code: 48465300-0000-11AA-AA11-00306543ECAC (Apple HFS/HFS+)
Partition unique GUID: 000043C0-3EEC-0000-B927-000090380000
First sector: 409640 (at 200.0 MiB)
Last sector: 1250001543 (at 596.0 GiB)
Partition size: 1249591904 sectors (595.9 GiB)
Attribute flags: 0000000000000000
Partition name: Customer
</pre>
Now the scary part - overwriting the partition map.
<pre style="background-color: #eee">
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed, possibly destroying your data? (Y/N): y
</pre>
Now reboot to get back to your Mac.
