If I put the program CD in, when it repairs, will that lose the vast number of updates that Microsoft have downloaded?
Yes - it will overwrite any files that have been downloaded via updates with the older originals from the disk.
Will I need to reload previous programs?
Not if you do a repair, but yes if you do a new installation.
Whatever you do, backup all data first. And downtime is worse than slowtime, as you rightly point out!
SD