Firstly, depending on the level 150 client you're refering to, it is indeed packed. You will need to unpack it. This can be done by viewing the program under hex and searching for the packer's signature which is generally located near the top. You can then google for an unpacker for the program in question. However, a good bit of unpackers fail. You can use Olly to manually unpack. I personally am not very adept with Olly, so I have no suggestions, but there are plenty of examples on the net which may guide you in the correct direction, i.e:
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After unpacking it, you must disable the exe's checksum for items. If I recall correctly, a good portion of these exe's have it disabled already.
Now, you can either move the entire item table, which is not what I recommend doing, or you can simple copy it and make another one. If you choose to move the entire table, you'll need to update a lot more pointers than you would if you simply made a copy and had it located towards the bottom. Pointers will still need to be updated mind you, but it's easier to do it that way. In fact, it's likely that the server.exe you're using has the item table at the bottom already.
Unfortunately, I do not know specific offsets or what pointers to update specifically so all I can do is provide general information in this case.
Whenever you add a new item, it must be added both client-side AND server-side. This applies to XP as well.
Good luck.