Help required with per minute data into half hourly data?

Hi,

First time posting here as I'm well and truly stuck.

I have a data (electrical current measured in Amps (A)) logger which logs data at pre determined intervals over the course of a project and once finished I can export this as an excel file. At the moment we have per minute data and we need to manipulate this data to something more tangable, let say half hourly and then send this data to a graph to compare before and after results based on a specific time in the project, for example the first two weeks and the last two weeks. This logger also measures across three phases, I1, I2 and I3.

Currently the amount of data is in the region of 43230 rows of data of which is as follows:
Time
I1 [A I2 [A] I3 [A]
1 08/08/2012 09:13:00 62 67 95
2 08/08/2012 09:14:00 60 61 89
3 08/08/2012 09:15:00 75 64 93

The time column consists of the date and the time which is the first problem, when I've tried to split it, it ends up with additional cells.

This may be very easy to sort first off but I also require this to be done on subsequent worksheets for other sites etc so a macro based approach may be suitable?

All comments would be greatly appriciated but bear in mind I'm no excel expert so go easy!