Drivers are written by the product manufacturer. Though Microsoft did provide generic support for many devices in W7 they are not responsible for making all printers/scanners, for example, work. If what your tech's are saying is accurate then Sharp did develop 64-bit drivers for that model but Toshiba/Lexmark did not for this new scanner. If I go to the Toshiba USA website and search the drivers link, it does not find any, not just none for 64bit - none period, so it seems there is an error on the webpage and I would contact them directly.
If the scanner truly does not have 64-bit drivers then it may be possible to use Virtual PC - XP mode to get it to function in an XP virtual window with 32bit drivers (which I also cannot find). Virtual PC - XP mode is a free download with Windows 7 Professional, Ultimate, and Enterprise.
UPDATE:
According to
this, the Lexmark XS463de works like a workstation and can scan documents to a network folder or email or FTP you the results and they can be viewed in a browser:
Scan to E-mail - With a single touch of a button, easily scan
your paper based documents to e-mail accounts or groups.
Seamlessly integrates into your corporate LDAP directory.
Scan to Desktop - Multiple ways to scan documents to a
PC/desktop. The scanned file can be sent to an individual
workstation via web browser, ScanBack utility, local or
network TWAIN driver or scan to network embedded solution.
Scan to FTP - Ideal way to archive and share large files with
multiple people.
Basically this printer/scanner is it's own computer and will do the work and then put the files where you want them; it seems to be designed to function from it's control panel. It doesn't seem like you would want to put a document on the scanner and then walk back to your desk and say import that now because it's designed for a networked environment and somebody could be over using the device in the time it takes you to return to your desk. Your techies can probably show you how to stand at the printer console, scan the document and tell it to store it on the network, send it in an email, or FTP it to a client. It does mention local or network twain driver but I don't know how it is meant to be used from your computer and I cannot find the drivers so you should contact the manufacturer for support in using it that way.