A lot of good advice here. There will be substantial amounts of EU money coming Bulgaria's way. The BG share of Regional development funding (the Cohesion Fund, ESF and ERDF) for 2007-2013 adds up to Eur 6.8 billion at todays prices (about Eur 900 per Bulgarian). There will also be substantial amounts from the "Preservation and Management of Natural Resources" part of the budget which includes the CAP. Much of this funding is targeted at areas which will greatly benefit Bulgaria, such as infrastructure (esp transport), employment, rural development, conservation (Natura 2000) and cross-border cooperation (Pelican's project ticks a couple of the right boxes here!). The way in which "pre-entry" EU money has been used (for example the redevelopment of Sofia Airport) shows the likely priorities.
The UK is unlikely to actually start spending 2007-2013 Regional development funding much before 2008. BG may be behind the UK in its planning and preparations.
There are particular problems with state/EU grants to employers and businesses since they distort the Single Market. This is partly why BG Air has been privatised. As Mat suggests, State Aids are a complex area and you need specialist advice on this.
EU funding is designed to supplement, not replace, domestic funding. It has to be "match funded" by private or public money according to fixed proportions. This is another reason why you will need BG partners.
Bidding for EU money is complex and needs to conform to regulations and policies. In the UK, it is common to use professional "bid writers", and as Mat advises, you would be wise to do the same.
The EU has to approve the spending plans of member states, and although the money is paid out by the governments, the spend is subject to audit by not only the EU itself but also the European Court of Auditors. The EU can and does take money back, including if it is not spent quickly enough (the "N" target).