Okay, you are just talking about the menus. It is interesting that on your computer just the menu items of the main menu use the large font.
I'm using UltraEdit v188.8.131.527 on Windows XP Prof. with SP3 with Windows Classic theme (not XP style) with all visual effects disabled for best performance and Office 2007 + all security hotfixes of Microsoft installed. Office 2007 installed the GDIPlus DLLs used also by UltraEdit. Additionally I have disabled the ClearType feature. Therefore UltraEdit uses for the menus, list boxes in the toolbars and the status bar the font Tahoma with size 8 pt as set in the Windows theme. With ClearType enabled the GDIPlus normally ignores the defined font in the Windows theme and use the ClearType font Segoe UI installed with Office 2007 and also used by Office 2007 independent of my Windows theme settings. Unfortunately UltraCompare uses font Segoe UI, too. I'm still waiting on the same fix for UC Prof. as IDM has done for UltraEdit on v184.108.40.2060. For details on the problem with font Segoe UI with ClearType not used see ClearType on UltraEdit 15
With my Windows display settings I can change the font size for the menus in the Windows display settings and the change is immediately applied after pressing button Apply (or OK) on the menus of UltraEdit as you can see on the attached screenshot as I increased the font size from 8 to 16 pt. Further I could see now that the font used for the Open File Tabs is the same as for the menus.
Because there is no setting in UltraEdit for changing the font size for the menus I suppose that the Windows GDI+ or a Windows display setting is responsible for that different font sizes. I suggest to save the current Windows display theme when not already done and play with all the font size settings. Maybe you can find out if one of them is responsible for the different font sizes in the UltraEdit menus. It may help to select and apply first a standard Windows display theme, and then change the settings to get what you want. I have already read a few times that this solved various display problems. One further note: on my computer when reloading and applying my saved display theme Windows XP always changes the sound theme from my preferred "No Sounds" to the standard Windows sound theme, and I have to select therefore always the sound theme "No Sounds" again after restoring my preferred display theme.