This code was taken from a TXT file I backup A LONG TIME AGO so if it embaresses me by looking retarded, just remember that PLEASE.
I don't have access to my current version of my source code and will not for at least a week. To be honest I havent touched the source code in a few months (she must be gagging for it) due to the lack of information of the data structures.
Remember; this will benefit the community (without compromising the integrity of the engines best kept secrets).

NOTE: I have since forgotten the meaning behind some data, such as bsp_blocks, which is just (in my case) and array of 20 32-bit integers.
NOTE: I do remember that this map only had 5 regions.
NOTE: I did my best using the manual.

Code:
////////////////////////////////////////////////////////////////
	// bsp_leafs
	typedef struct {
		unsigned long type; // root = 0xFFFFFF80, child = 0xFFFFFF00
		long  region;
		float plane[4];
		long  _unused_;
		long  lBlockIndex; // x = block offset
		long  lNumBlocks; // y = num blocks
	} WMB7_BSP_LEAFS;
	// NOTE: x+y = next leaf x
	// x = block offset
	// y = num blocks
	WMB7_BSP_LEAFS bsp_leafs[5];
	// NOTE: Number of leafs = Number of regions
	// Each leaf is 36 bytes. There is always one leaf (the root) even without BSP.
	file.Seek(header.bsp_leafs.offset);
	file.Read(&bsp_leafs, header.bsp_leafs.length);
	////////////////////////////////////////////////////////////////
	// bsp_blocks
	typedef struct {
		long a;
		long unused0; // 0
		float c[3];
		long unused1; // 0
		long next; // ?
		long prev; // ?
		long lSurfaceOffset; // ?
		long lVisibleSurfaces; // ?
	} WMB7_BSP_NODES;
	WMB7_BSP_NODES bsp_nodes[15];
	file.Seek(header.bsp_nodes.offset);
	file.Read(&bsp_nodes, header.bsp_nodes.length);
	////////////////////////////////////////////////////////////////
	// aabb_hulls
	file.Skip(header.aabb_hulls.length);
	////////////////////////////////////////////////////////////////
	// bsp_blocks
	unsigned long bsp_blocks[20];
	file.Seek(header.bsp_blocks.offset);
	file.Read(&bsp_blocks, header.bsp_blocks.length);
	////////////////////////////////////////////////////////////////
	// pvs
	file.Skip(header.pvs.length);
	////////////////////////////////////////////////////////////////
	// objects
	file.Skip(header.objects.length);
	////////////////////////////////////////////////////////////////


Many, many thanks!