"The Commission will then examine all arguments," said Mario Monti, the European Commissioner for Competition Issues.
Microsoft submitted its written response to the latest antitrust case on 16 November. Antitrust officials are currently examining that reply.
Monti reiterated that the European lawsuit is distinct from Microsoft's antitrust case in the US, but conceded that there are similarities.
Microsoft is fighting accusations that it violated European antitrust rules by using illegal practices to extend its dominant position in the PC operating system market into the low-end server operating system market.
The European Commission defines low-end server systems as cheaper servers usually used as file and print servers, as well as Web servers.
This case is the result of two separate antitrust investigations into Microsoft. The first case was sparked by a complaint from rival Sun Microsystems in 1998, which alleged that Microsoft was using its Windows operating system software to muscle rivals out of the market for server software.
The case focused on Microsoft's alleged discriminatory licensing and the company's refusal to supply data to allow for the interoperability of rival server products with older versions of Windows.
In February 2000, the commission launched a separate investigation to see if Microsoft was doing the same thing with Windows 2000.
As with the first case, the commission believes Microsoft may have withheld key interoperability information that other server software vendors needed to allow their products to communicate with Microsoft's dominant PC and server software products.