You can export your email and address book from within Outlook Express File menu and tyhen save them to floppies etc.
If you open My Computer and double click Dial Up networking, you'll see your ISP connection. Right click it and drag it to the desktop, selecting Copy Here. The copy will change to a file with a .dun extension, and teh file can be read in Notepad. Save that file to a floppy and on your new computer, drag it back into Dial Up networking and it will change back to your ISP connection.. You may need to reset your password though.
On the performance issue, with a computer of that age I'd advise you to format the hard drive and re-install Windows to have a fresh start, That will restore the performance.