I had a long response forming in my head, but had a meeting to go to, so now I'll go with a short response.
1. 6 weeks is plenty of time if you are like me.
2. Cut back on cycling, maybe 1/2 your normal amount.
3. Start swimming, maybe every other day, preferably similar to what race will be like. lake, ocean, pool, whatever. Don't worry about how you look or whatever, just get in the water and go. It'll get better, don't worry. 1/4mile is short.
4. Just start running more. Maybe 3 or 4 days a week. Try mixing in a brick once a week (hard bike then run). If you can, try to add some speed workouts to get your average mile time to improve more. Like swimming, just doing it will make vast improvements.
5. Train hard, but don't injure yourself. If something hurts, don't force it. Then give yourself a few days to rest/taper before the race so you don't go into the race with sore legs or something.
Those are all tips I've come up with from the training i did this summer. I decided to do my first tri with about 4-5 weeks of good training. I was/am a good cyclist, but never did distance swimming, and used to run but not much anymore.
Come race day, just go fast! It's a short race, you'll survive. Survive the swim as best you can, then haul through the transition and get to what you know you are good at. Don't kill yourself on the bike, but make sure you are passing people! And you will if you have good race experience, which it sounds like you do. I spent my whole bike leg in the race passing lots of people, and was going hard the whole time. Once you hit the run, do what you can. Anything under 8 minute miles average will probably place you a bit above the middle places in that part of the race, you'd be suprised. Closer to 7 minute miles will be very good I think.