Please help i've never grown sweetpeas and wasn't sure what to expect when I chucked the seeds that had started to grow in the packet in with the ones i'd started already and now they have all grown to about 2ft already all 3 packets and the pot is over crowded but I don't know if I should risk planting them in the Garden now or wait till the weather is better
If you are going into winter in the northern hemisphere, sweet peas are usually planted as seeds directly in the ground outside. You probably would do better just getting more seeds and direct sowing. In the southeast US they are usually sown in November or December. As you get further north (Mid-Atlantic or northeastern US for instance) sweet peas are usually planted in late winter - ~February (again, direct in ground as seed).
In the southern hemisphere going into spring it MIGHT be possible to move the plants outdoors. Success rate will probably not be very high due to the amount of growth already. Best method would be to pinch them back hard, then gradually harden them off (daily increase of time outdoors in increased light and cold) and then transplant into the ground.
As above, knowing where you are growing them will result in much better answers. All gardening is local.
A good article on sweet peas is http://aggie-horticulture.tamu.edu/newsletters/hortupdate/hortupdate_archives/2005/mar05/Sweetpea2.html
Edit: just saw that all the plants are in one pot - this reduces success rate from transplanting further as at 2 feet tall their roots are completely entangled. You won't be able to separate the plants. Best bet there would be to cut off all but 2 or 3 stems at ground level, and follow the other suggestion for hardening etc. Or, better still, go with direct sowing.