Open Explorer to the size you want, go into your file&Folder options (tools menu) or from control panel. enable remember windows positions and leave windows open (worded differently i fink..sorry not at xp machine at the moment)
close the file/folders options window, and leave Explorer open.
Do a reboot leaving the Explorer window open, and once you've rebooted explorer should appear in same position, you can close it now. Now everytime you open it it remembers the size and position. But if you move the folder or resize it again, then it will remember those changes.
If you meant Internet Explorer, open IE, size it how you want and click afew links you already have (do not resize ie window).
Then close IE, and when you reopen it it will remember size & position.