Capital gains tax will be set at a flat rate of 18% independent of income. Additionally benefits from taper relief and indexation allowance will expire on 5th April 2008.
In addition for share sales from 5th April 2008 onwards (the 08-09 tax year) the Chancellor has made some changes. These are described towards the end of this draft explanatory document. Basically trades on the same day are handled the same way as before as are share purchases within 30 days following a sell. However if the sell has not been matched by either a same day trade or a purchase in the following 30 days then unmatched buy trades preceding the date of the sell are merged into a single holding, effectively a single buy trade, called a section 104 holding. Heres an example of how a section 104 holding is handled.
See also this capital gains faq for info on the new changes.