Disk management shows different drive capacity from windows explorer

Check if any hidden files are on the disk.
Could be Vista ShadowStorage restore points.

That's a great article, thanks for the link!

What OS and SP level are you running? IIRC earlier SP levels of XP don't handle 2TB disks...

Actually, I suspect Service Packs on XP is not the issue. As evongugg says, the 28-bit LBA limit was 137 GB by HDD maker's numbers, and M$ calls that 128 GB. 48-bit LBA Support solved that limit problem. But OP says his Explorer indicates 181 GB. That ain't 128, which is the usual indicator. Moreover, it is larger than 128 GB, so I don't see how Explorer under original XP could come up with that number.

I think we need clearer info on what Disk Manager is showing. Of the two right-hand panes there, does this HDD show up both in the upper and lower panes? In the lower right-hand pane, does the unit show as one block with a size of 1863 GB? Does it have a letter assigned as its name? Or, is that block shown as an 1863 GB block that contains in it a smaller named block of size 181 GB, plus a whole big bunch of Unallocated Space? Your Explorer info suggests that the big drive has only one Partition established on it with a size of 181 GB, and more unused space.

When you run Seatools for DOS, what does it show you as the maximum Logical Block Address?

Seagate built into many of their HDD's a system to limit the disk's usable size for compatibility with older hardware. You can use Seatools for DOS to re-specify the maximum LBA address it will use, and that will be stored in the HDD's firmware. From then on the whole world believes it is this new smaller size. For example, I installed a 160 GB HDD from Seagate in an older system that cannot be upgraded to the newer "48-bit LBA Support" system, so it had to be limited to the 137 GB max size. I used Seatools to specify that its maximum Logical Block number is 268,435,456 blocks. At 512 bytes per sector, that comes to 137,438,953,472 bytes and no hardware or software can force that disk to go beyond that.

As part of this system, in the same area of Seatools, Seagate built in an undo tool: you can tell it to restore the hard drive to its original true full capacity, whatever that is. For a 2 TB drive it is probably around 4,294,967,296 Logical Blocks, which could give you 2,199,023,255,552 bytes max.

So, use Seatools' utility for this and look closely at what it says it has for the maximum number of Logical Blocks. It should be around 4 billion. If it's set to more like 2 billion, that would explain less than 1 TB. Assuming the disk is empty and you are not trying to use any of its data, use the Seatools utility to restore its full capacity.

If that is not the issue, it's back to looking at what Windows is doing.

Good, Seatools confirms the disk is set up right at the hardware level. Still, it's frustrating that they don't work as expected. Hate to say it, but two disks treated identically and exhibiting identical problems suggest you did something wrong both times - I have no idea what! It's just unusual for two drives to show identical problems if they both are manufacturer's issues. Not impossible, of course! But you are doing the right thing. If you contact Seagate for help or RMA services, the first thing they will want is the results of Seatools runs, so save them.

Actually there is no problem with your hard drive, the reason Windows shows less capacity on your drive relies on the way formatted (NTFS, FAT, etc) drives work.

From: http://en.wikipedia.org/wiki/Hard_disk_drive

Which totally satisfies your situation (2TB * 0.91 = 1.82TB)