There aren't (or shouldn't be) any packets that change that portion of the client. They've had this problem in the past, and it was a conflict between the "absolute" positioning of the control in the INI files in regards to DirectX 9 (the highest supported DirectX version of XP) whereas Windows 7 is DirectX 11 (or sometimes 10) by default. Between Dx9 and Dx11, a lot of things were changed. Some legacy applications no longer worked, and some new applications weren't supported by people still using 9. It was one of the many ways Microsoft pushed Windows XP towards being obsolete.
Anyway, check the official TQ forum. Most likely the complains will cause a patch to be released within the next week or two if it truly is a problem with everyone on XP. And also in that case, there's no real point having this thread here, if it's not something that can be fixed on our end.