EasybCD is just a program, not the boot loader itself. MS's bootmgr is what is in charge here.
The easiest way to get it where XP's boot loader (ntldr) is in charge is to use EasyBCD. With it installed go to Bootloader Setup > MBR Configuration Options > Install the Windows XP bootloader to the MBR > Write MBR.
Reboot to make sure the menu is gone and XP is booting correctly. Now you can uninstall EasyBCD.
Your goal is to get rid of Windows 7, right? If not, than you well need to keep your current boot loader. Hiding the menu is simple as changing the timeout to 0. With this timeout the default entry would be selected immediately.