Colds and flus are caused by viruses and these are very simple creatures that due to their very simplicity they are difficult to fight. Bacteria are a lot more complex and easier to sabotage using one antibiotic or other. All one can do is let them run their course though some think that vitamin C can help speed up the recovery process.
I don't get that many colds recently. I had one in 2005 after I got soaked in the rain, none in 2006 and one over this weekend that suddenly disappeared on Monday evening. Either my immune system got stronger due to exercising and eating a lot of fruit and veg or else the virus I got was a weak one.