Lindose.A is a new virus that can infect both Windows and Linux. In practical terms, it is not a threat, more a "proof of concept", but more damaging viruses of this type are likely to follow. The truth is that no general-purpose computing platform is immune to viruses.
W32.Magistr.24876@mm is a more serious threat. It is a mass-mailing worm that was found in-the-wild during the middle of March 2001 and it is currently near the top of MessageLabs' list of viruses caught (http://www.messagelabs.com/viruseye/). One month after it infects a machine, it might activate, overwriting files on all accessible drives. Therefore, we will probably see it activating on the first machines it infected about now. This is another reason to make sure your anti-virus software is properly updated.