I think to get parents involved in the classroom can be somewhat difficult just because most parents work during the school day. But I think it would be a good idea to have an evening even for all parents and let them know about volunteer opportunities that are available. Also, you can let them let you know what times are best for them instead of you giving them times specific. Try to work around their schedules and see when they can make it in to help out.
Don't forget about the parents who can't come in because of work or other situations. I think having a blog or wiki where you post about what is going on in the classroom, student work and educational links will help extend your classroom into the virtual space. Getting parents to learn about the blog and make comments takes work (not a one night parent information sessions - I know from experience :) ), but you could approach it as a way they can volunteer with your class. Research shows that parents who talk with their kids about school tend to do better academically. In fact, the research I read mentions that the conversations at home seem to show more correlation with academic achievement than having parents volunteer physically within the school. Here is a link to a report that summarizes research in the area of parental involvement.
Great idea to involve parents but as a new teacher you should proceed with care when it comes to parents volunteering in your classroom and implement an "open door policy" gradually over time. Unfortunately, there are some parents who mean well but can actually be disruptive in the classroom and in some families one parent is not allowed to have contact with his/her child.
Make sure you check with school administration regarding background checks/ fingerprinting policies for volunteers and adults who will be spending extended time working with children in your classroom. Here in NY State my son had to be fingerprinted before starting his second year of college ( secondary science ed ) because they would be visiting schools and observing classes for an extended period of time during the upcoming semester.
When you first start teaching check with other teachers in your school regarding recommended parent helpers and you can recruit them directly rather then inviting everyone and finding yourself in an awkward situation where you may have to decline an offer of assistance.
Projects are a great way to get parents more involved at home. I have been using a 3D Memorial Project for several years and this provides a great opportunity for parents to work with their children. Several students have actually learned more about their family history and created a Memorial for a member of their family....
Having parents volunteer in the classroom is a great idea, but proceed with caution. First of all, you need to identify your reason for having parents in the classroom. Will they come in to simply observe? (which I would not recommend) Will they be there to provide general help? Will they have a specific assignment or task? Once you know "why" parents are coming to volunteer, you can think about "how" you want them to do it.
I have had the most success with parents in the classroom when they are coming into do a specific task and have been given specific guidelines from me. For example, I might have a parent come in to staff a science center where kids are observing & drawing plants and need direction and guidance. Before coming in, I would give that parent a list of do's and dont's, questions they could ask the kids, etc. Things tend to run more smoothly this way.
I also want to second what Johnathan had to say - check with your school and find out the policies that govern parent/student contact. Many schools now put parents through some kind of background check before they are allowed to help in the classroom or go on field trips.